California and the Clean Air Act (CAA) Waiver: Frequently Asked Questions
Congressional research reportMay 9, 2025
Ask Donna
What actually matters in this document.
Text
California and the Clean Air Act (CAA)
Waiver: Frequently Asked Questions
Updated May 9, 2025
Congressional Research Service
https://crsreports.congress.gov
R48168
SUMMARY
California and the Clean Air Act (CAA) Waiver:
Frequently Asked Questions
In the Air Quality Act of 1967 (P.L. 90-148), later amended to the Clean Air Act (CAA; codified
at 42 U.S.C. §§7401 et seq.), Congress preempted state governments from adopting their own air
pollutant emissions standards for new motor vehicles and new motor vehicle engines.
Notwithstanding, Congress decided to provide an exemption for the State of California. Under
CAA Section 209, California can apply to the U.S. Environmental Protection Agency (EPA) for a
waiver from the federal preemption, and EPA is to grant this waiver absent certain disqualifying
conditions. As of 2025, California has used this authority to receive more than 100 federal
preemption waivers for new and amended state-level vehicle emissions standards. Further, in the
CAA Amendments of 1990 (P.L. 101-549), Congress allowed other states to adopt California’s
vehicle emissions standards under certain conditions. As of 2025, 17 states and the District of
Columbia have used the authority under CAA Section 177 to adopt some subset of California’s
standards. California estimates that itself and these “Section 177 States” accounted for more than
40% of new light-duty vehicle registrations and 25% of new heavy-duty vehicle registrations in
the United States in 2023.
R48168
May 9, 2025
Benjamin M. Barczewski
Legislative Attorney
Kathryn G. Kynett
Analyst in Environmental
Policy
Emily N. Peterson
Research Librarian
Congress initially provided California with the federal preemption waiver authority because the state had “demonstrated
compelling and extraordinary circumstances sufficiently different from the Nation as a whole to justify standards on
automobile emissions which may, from time to time, need to be more stringent than national standards.” Further, some in
Congress believed that California’s “pioneering” efforts “offer[ed] a unique laboratory, with all the resources necessary, to
develop effective control devices which can become a part of the resources of this Nation.” For several decades, California’s
authority went unchallenged. However, beginning in the late 2000s, federal, state, and local governments, Congress, and
stakeholder groups began to debate more heavily the impact of California’s federal preemption waiver authority on matters
such as consumer markets, industry economics, public health and welfare, and the environment, among other items. Congress
continues to be interested in many issues associated with this authority, including its potential effects on state sovereignty,
cooperative federalism, interstate commerce, U.S. energy and industrial policy, international trade and competitiveness,
public health, air quality, and climate change
In January 2025, EPA granted preemption waivers or authorizations for California’s Advanced Clean Cars II regulation,
Heavy-Duty Low NOX (nitrogen oxide) Omnibus regulation, Small Off-Road Engine (SORE) amendments, and In-Use OffRoad Diesel-Fueled Fleets amendments. That same month, EPA also granted partial authorizations for California’s
Commercial Harbor Craft amendments and Transport Refiguration Unit (TRU) amendments. California withdrew requests
for authorizations for the provisions within these regulations EPA did not act on. In addition, California withdrew its requests
for a waiver for its Advanced Clean Fleets (ACF) and an authorization for its In-Use Locomotive regulation.
In April 2025, some Members of Congress introduced Congressional Review Act resolutions disapproving EPA’s decisions
to grant waivers for the following: Advanced Clean Cars II (ACC II) (H.J.Res 88; S.J.Res. 45), Heavy-Duty Omnibus Low
NOX (H.J.Res 89; S.J.Res. 47), and Advanced Clean Trucks (H.J.Res 87; S.J.Res. 46). On April 30 and May 1, 2025, the
House voted to adopt H.J.Res 88, H.J.Res 89, and H.J.Res 87.
As of April 2025, three bills have been introduced in the 119th Congress seeking to modify or revoke California’s federal
preemption waiver authority under CAA Section 209 (b). Similar proposals were introduced in the 118th and 117th
Congresses.
•
H.R. 346 and S. 996: Preserving Choice in Vehicle Purchases Act. H.R. 346 would amend Section 209(b)
of the CAA to prohibit EPA from issuing waivers to states that directly or indirectly limit the sale or use of
new motor vehicles with internal combustion engines. In addition, the bill would require EPA to revoke
waivers granted between January 2022 and the date of the enactment of the bill. The House version was
introduced on January 13, 2025, and the Senate version on March 12, 2025.
•
H.R. 2218: Stop California from Advancing Regulatory Burden Act of 2025 (Stop CARB Act of 2025).
H.R. 2218 would amend Section 209(b) of the CAA by repealing the waiver authority allowing California
to adopt or attempt to enforce emission control standards on new motor vehicles. In addition, the bill would
Congressional Research Service
California and the Clean Air Act (CAA) Waiver: Frequently Asked Questions
prohibit state-level emissions standards for nonroad engines and vehicles. The bill would nullify existing
waivers and deny any pending applications. It was introduced on March 18, 2025.
http://www.congress.gov/cgi-lis/bdquery/z?d117:H.R.8773:
Congressional Research Service
California and the Clean Air Act (CAA) Waiver: Frequently Asked Questions
Contents
What Is the U.S. Environmental Protection Agency’s (EPA’s) Authority to Regulate Air
Pollutant and Greenhouse Gas (GHG) Emissions from Mobile Sources? ................................... 1
What Is California’s Authority to Regulate Air Pollutant and Greenhouse Gas Emissions
from Mobile Sources? .................................................................................................................. 2
What Is Federal Preemption of State Vehicle Emissions Standards? .............................................. 3
What Is the Clean Air Act Waiver?.................................................................................................. 4
Preemption of State Emissions Standards for New Motor Vehicles or New Motor
Vehicle Engines ...................................................................................................................... 4
Preemption of State Emissions Standards for New Nonroad Vehicles or New Nonroad
Vehicle Engines ...................................................................................................................... 5
California’s Waivers and Authorizations ................................................................................... 5
What Is the Process by Which California Applies for a Waiver? .................................................... 6
How Can Other States Adopt California’s Vehicle Standards? ....................................................... 7
What is the Status of California’s Waiver Requests? ...................................................................... 9
Heavy-Duty Omnibus Low NOX Waiver Request .................................................................. 10
Small Off-Road Engine (SORE) Authorization Request ........................................................ 10
Transport Refrigeration Unit Authorization Request ............................................................... 11
Commercial Harbor Craft Authorization Request .................................................................... 11
Advanced Clean Cars II Waiver Request ................................................................................ 12
In-Use Off-Road Diesel-Fueled Fleets Authorization Request ............................................... 12
In-Use Locomotive Authorization Request ............................................................................. 12
Advanced Clean Fleets Waiver Request.................................................................................. 13
Advanced Clean Trucks .......................................................................................................... 13
What Is the History of California’s Clean Air Act Waivers for Motor Vehicle GHG
Emissions?.................................................................................................................................. 14
Actions Under the Bush Administration ................................................................................. 14
Actions Under the Obama Administration .............................................................................. 14
Actions Under the First Trump Administration....................................................................... 16
NHTSA’s Interpretation of EPCA Preemption.................................................................. 16
EPA’s Interpretation of Section 209(b) ............................................................................. 18
EPA’s Interpretation of Section 177 .................................................................................. 19
Actions Under the Biden Administration ................................................................................ 19
EPA’s and NHTSA’s Reinterpretation of EPCA Preemption ............................................ 20
EPA’s Reinterpretation of Section 209(b)(1)(B): “Compelling and Extraordinary
Conditions” .................................................................................................................... 21
EPA’s Reinterpretation of Section 177 .............................................................................. 22
Actions Under the Second Trump Administration .................................................................. 22
What Actions Has Congress Taken Regarding the Waiver Authority?.......................................... 23
119th Congress ......................................................................................................................... 23
H.R. 346: Preserving Choice in Vehicle Purchases Act .................................................... 23
S. 996: Preserving Choice in Vehicle Purchases Act of 2025 ........................................... 23
H.R. 2218: Stop California from Advancing Regulatory Burden Act of 2025 (Stop
CARB Act of 2025) ....................................................................................................... 23
th
118 Congress ......................................................................................................................... 24
H.R. 1435: Preserving Choice in Vehicle Purchases Act .................................................. 24
Congressional Research Service
California and the Clean Air Act (CAA) Waiver: Frequently Asked Questions
H.R. 4468: Choice in Automobile Retail Sales Act of 2023 ............................................. 26
S. 2090: Preserving Choice in Vehicle Purchases Act of 2023 ......................................... 26
117th Congress ............................................................................................................................... 26
H.R. 8773: Revoking Engine and Vehicle Requirements Act of 2022 .................................... 26
Can Clean Air Act Waivers Be Reviewed Under the Congressional Review Act? ....................... 26
What Actions Have Been Taken in the Federal Courts Regarding the Waiver? ............................ 29
The Constitutionality of Section 209(b): The Equal Sovereignty Doctrine ............................ 30
Conflicts with the Energy Policy and Conservation Act (EPCA) and California
Regulation of GHGs............................................................................................................. 32
Pending Litigation: Western States Trucking Association, Inc. v. EPA.................................... 33
Figures
Figure 1. States That Have Adopted a Selection of California’s Motor Vehicle Standards ............. 8
Contacts
Author Information........................................................................................................................ 35
Congressional Research Service
California and the Clean Air Act (CAA) Waiver: Frequently Asked Questions
his report examines some of the frequently asked questions regarding California’s federal
preemption waiver authority for new vehicle emissions standards, including its origin,
purpose, history, and regulatory process. This report also reviews associated actions by
California, other states, the executive branch, Congress, and the federal courts.
T
What Is the U.S. Environmental Protection Agency’s
(EPA’s) Authority to Regulate Air Pollutant and
Greenhouse Gas (GHG) Emissions from Mobile
Sources?
The U.S. Environmental Protection Agency (EPA) derives its authority to regulate air pollutant
and greenhouse gas (GHG) emissions from mobile sources from Section 202 of the Clean Air Act
(CAA), as amended.1
CAA Section 202(a) requires EPA to establish standards for emissions of air pollutants from new
motor vehicles2 or new motor vehicle engines that, in the EPA administrator’s judgment, cause or
contribute to air pollution that may reasonably be anticipated to endanger public health or
welfare. Standards under Section 202 must also take into account issues such as technological
feasibility, the cost of compliance, useful life of the vehicle, and industry lead time, among other
items.3
EPA has promulgated standards on new motor vehicles and new motor vehicle engines for
emissions of nonmethane organic gases (NMOGs), nitrogen oxides (NOX), particulate matter
(PM), carbon monoxide (CO), and formaldehyde (a proxy for air toxics in general).4 Other
sections of the CAA require EPA to set standards for different types of mobile sources (e.g.,
locomotives, marine vessels, small off-road engines, and aircraft, among others).5
In the 2007 decision Massachusetts v. EPA, the Supreme Court held that EPA has the authority to
regulate GHG emissions from new motor vehicles or new motor vehicle engines as “air
pollutants” under CAA Section 202.6 In the 5-4 decision, the Court’s majority concluded that EPA
must either decide whether GHG emissions from new motor vehicles contribute to air pollution
that may reasonably be anticipated to endanger public health or welfare or provide a reasonable
explanation why it cannot or will not make that decision.
1 42 U.S.C. §7521.
2 The term motor vehicle means any self-propelled vehicle designed for transporting persons or property on a street or
highway. 42 U.S.C. §7550(2).
3 42 U.S.C. §7521(a).
4 40 C.F.R. Subchapter C, Part 86; 40 C.F.R. Subchapter U. For more discussion of these standards, see CRS In Focus
IF12433, Automobiles, Air Pollution, and Climate Change, by Richard K. Lattanzio (2024).
5 For example, 42 U.S.C. §7547; 42 U.S.C. §7571.
6 Massachusetts v. EPA, 549 U.S. 497, 528-529 (2007). The majority held that “[t]he Clean Air Act’s sweeping
definition of ‘air pollutant’ includes ‘any air pollution agent or combination of such agents, including any physical,
chemical ... substance or matter which is emitted into or otherwise enters the ambient air.... ’ ... Carbon dioxide,
methane, nitrous oxide, and hydrofluorocarbons are without a doubt ‘physical [and] chemical ... substances[s] which
[are] emitted into ... the ambient air.’ The statute is unambiguous” (pp. 528-529).
Congressional Research Service
1
California and the Clean Air Act (CAA) Waiver: Frequently Asked Questions
In December 2009, EPA promulgated findings that GHGs endanger both public health and
welfare and that GHG emissions from new motor vehicles contribute to that endangerment.7 With
these findings, the CAA required EPA to establish GHG standards for the contributing sources.
EPA has since promulgated standards on new motor vehicles for emissions of carbon dioxide
(CO2), methane (CH4), and nitrous oxide (N2O).8
What Is California’s Authority to Regulate Air
Pollutant and Greenhouse Gas Emissions from
Mobile Sources?
The State of California derives its authority to regulate air pollutant and GHG emissions from
mobile sources through a variety of state statutes within the bounds set by the federal CAA.
In 1959, prior to the enactment of the CAA, California enacted legislation requiring the State
Department of Public Health to establish air quality standards and necessary controls for motor
vehicles.9
It shall be the duty of the State Director of Public Health to determine by February 1, 1960,
the maximum allowable standards of emissions of exhaust contaminants from motor
vehicles which are compatible with the preservation of public health including prevention
of irritation to the senses.10
In developing the ensuing standards, the Department of Public Health was required under state
law to hold hearings with public notice and provide opportunities for interested persons to
participate. As directed, the Department of Public Health—then later the Motor Vehicle Pollution
Control Board and the California Air Resources Board (CARB)—developed the country’s first set
of vehicle emissions standards during the 1960s, including crankcase requirements11 and exhaust
emissions standards. These state standards came prior to the enactment of the CAA.
In the decades that have followed the enactment of the CAA, CARB has adopted, implemented,
and enforced a wide array of state-level mobile source air pollution controls within the bounds set
by the CAA.12
In July 2002, California became the first state to enact legislation requiring reductions of GHG
emissions from new motor vehicles. The legislation, Assembly Bill (AB) 1493, required CARB to
adopt regulations requiring the “maximum feasible and cost-effective reduction” of GHG
7 U.S. Environmental Protection Agency (EPA), “Endangerment and Cause or Contribute Findings for Greenhouse
Gases Under Section 202(a) of the Clean Air Act; Final Rule,” 74 Federal Register 66496, December 15, 2009.
Although generally referred to as simply “the endangerment finding,” it comprised two separate findings finalized by
the EPA administrator: (1) a finding that six greenhouse gases (GHGs) endanger public health and welfare, and (2) a
separate “cause or contribute” finding that the combined emissions of GHGs from new motor vehicles and new motor
vehicle engines contribute to the GHG pollution that endangers public health and welfare.
8 40 C.F.R. Subchapter C, Part 86. For more discussion of these standards, see CRS In Focus IF12433, Automobiles,
Air Pollution, and Climate Change, by Richard K. Lattanzio (2024).
9 Ch. 200, §1, Cal. Stats. Regular Session, 1959, p. 2091, https://clerk.assembly.ca.gov/sites/clerk.assembly.ca.gov/
files/archive/Statutes/1959/59Vol1_59Chapters.pdf.
10 Ibid.
11 Crankcase emissions are defined as airborne substances emitted to the atmosphere from any part of the engine
crankcase’s ventilation or lubrication systems. The crankcase is the housing for the crankshaft and other related internal
parts (40 C.F.R. §1042.901). These emissions are separate from engine exhaust, or tailpipe, emissions.
12 See Cal. Health and Safety Code, Division 26, Part 5.
Congressional Research Service
2
California and the Clean Air Act (CAA) Waiver: Frequently Asked Questions
emissions from any vehicle whose primary use is noncommercial personal transportation.13 The
reductions applied to motor vehicles manufactured in model year (MY) 2009 and thereafter.
Under this authority, CARB adopted regulations in September 2004 and subsequently
implemented and enforced them within the bounds set by the federal CAA.
What Is Federal Preemption of State Vehicle
Emissions Standards?
The concept of federal preemption arises from the Supremacy Clause of the Constitution. The
Supremacy Clause declares federal law (including the Constitution, treaties, and statutes) to be
“the supreme Law of the Land.”14 Federal law, accordingly, supersedes or displaces inconsistent
or conflicting state laws.15 Through statutory enactments, Congress can preempt state laws or
regulations within a field entirely, preempt only state laws or regulations that conflict with federal
law, allow states to seek a waiver from a preemption, or allow states to act freely.16
In the Air Quality Act of 1967 (P.L. 90-148), later amended to the CAA, Congress preempted
states from adopting their own emissions standards for new motor vehicles or new motor vehicle
engines (i.e., for those vehicles driven on streets or highways). CAA Section 209(a) provides that
No State or any political subdivision thereof shall adopt or attempt to enforce any standard
relating to the control of emissions from new motor vehicles or new motor vehicle engines
subject to this part. No State shall require certification, inspection, or any other approval
relating to the control of emissions from any new motor vehicle or new motor vehicle
engine as condition precedent to the initial retail sale, titling (if any), or registration of such
motor vehicle, motor vehicle engine, or equipment.17
This preemption allows automakers some level of nationwide regulatory certainty and a remit
from the possibility of a “patchwork quilt” of numerous and differing state-level regulatory
programs for emissions from newly manufactured motor vehicles or newly manufactured motor
vehicle engines.18 States do retain the right to control, regulate, or restrict the use, operation, or
13 Ch. 200, Sec. 3(a), Cal. Stats. Regular Session, 2002, p. 867 (codified at Cal. Health and Safety Code §43018.5),
https://clerk.assembly.ca.gov/sites/clerk.assembly.ca.gov/files/archive/Statutes/2002/2002_Statutes_1667_Vol_1.pdf.
The legislation required that the vehicle emissions standards achieve “the maximum feasible and cost-effective
reduction of greenhouse gas emissions from motor vehicles” while accounting for “environmental, economic, social,
and technological factors.”
14 U.S. Const. art. VI.
15 See CRS, “Overview of Supremacy Clause,” Constitution Annotated, https://constitution.congress.gov/browse/essay/
artVI-C2-1/ALDE_00013395/, accessed April 30, 2025.
16 Gade v. Nat’l Solid Wastes Mgmt. Assn., 505 U.S. 88, 98 (1992). Congress can disavow an intent to preempt certain
categories of state law by including a “savings clause” to that effect in federal statutes (see, e.g., 29 U.S.C. §1144(b)) or
by allowing federal administrative agencies to grant “preemption waivers” to states in certain circumstances (see 42
U.S.C. §7543(b)).
17 42 U.S.C. §7543(a). See also S. Rept. 91-1196, at 32 (1970).
18 The term new motor vehicle means “a motor vehicle the equitable or legal title to which has never been transferred to
an ultimate purchaser”; the term new motor vehicle engine means “an engine in a new motor vehicle or a motor vehicle
engine the equitable or legal title to which has never been transferred to the ultimate purchaser”; and with respect to
imported vehicles or engines, such terms mean “a motor vehicle and engine, respectively, manufactured after the
effective date of a regulation issued under section 7521 which is applicable to such vehicle or engine (or which would
be applicable to such vehicle or engine had it been manufactured for importation into the United States).” 42 U.S.C.
§7550(3).
Congressional Research Service
3
California and the Clean Air Act (CAA) Waiver: Frequently Asked Questions
movement of registered or licensed motor vehicles within their jurisdiction, and many have statelevel laws to these effects.19
What Is the Clean Air Act Waiver?
Under CAA Sections 209(b) and 209(e), California may request a waiver or authorization20 from
federal preemption of state-level regulatory programs for emissions from new motor vehicles or
their engines or new nonroad vehicles or their engines.21 EPA must grant the CAA waiver before
California’s rules may be enforced.
Preemption of State Emissions Standards for New Motor Vehicles
or New Motor Vehicle Engines
Although the initial congressional discussions during the drafting the Air Quality Act of 1967
favored preempting new motor vehicle emissions standards in all 50 states, the California
congressional delegation negotiated a special exception for California. They argued for this
exemption because of California’s local and regional air pollution challenges and pioneering
efforts in regulating vehicle emissions.22 At that time, Congress concluded that
although the situation may change, in the 15 years that auto emissions standards have been
debated and discussed, only the State of California has demonstrated compelling and
extraordinary circumstances sufficiently different from the Nation as a whole to justify
standards on automobile emissions which may, from time to time, need to be more stringent
than national standards.23
Further, Representative John E. Moss of California stated that continuation of California’s
“pioneering” efforts “offer[s] a unique laboratory, with all the resources necessary, to develop
effective control devices which can become a part of the resources of this Nation.”24
Thus, CAA Section 209(b) provides that
[t]he [EPA] Administrator shall, after notice and opportunity for public hearing, waive
application of this section [the preemption of State emissions standards] to any State which
has adopted standards (other than crankcase emission standards) for the control of
emissions from new motor vehicles or new motor vehicle engines prior to March 30, 1966,
if the State determines that the State standards will be, in the aggregate, at least as protective
of public health and welfare as applicable Federal standards.25
19 42 U.S.C. §7543(d).
20 Section 209(b) of the Clean Air Act refers to the permission EPA may grant California to enforce its own emissions
standards for on-road vehicles as a “waiver” of preemption, while Section 209(e) permits EPA to “authorize”
California to enforce its own emissions standards for nonroad vehicles. 42 U.S.C. §7543(b), (e)(2)(A). Although
Congress used different terms, the action the CAA permits EPA to take with regard to on-road and nonroad vehicles is
the same. As a result, CRS uses the terminology of “waiver” and “authorization” in a similar method throughout this
report.
21 42 U.S.C. §7543(b) and (e).
22 For a short history of California’s air pollution challenges and mitigation actions, see California Air Resources
Board, “History,” https://ww2.arb.ca.gov/about/history.
23 113 Cong. Rec. 30975, 1967. For additional history behind CAA Section 209(b), see National Academies of
Sciences, Engineering, and Medicine, State and Federal Standards for Mobile-Source Emissions (Washington, DC:
National Academies Press, 2006), https://doi.org/10.17226/11586.
24 113 Cong. Rec. 30975, 1967.
25 42 U.S.C. §7543(b)(1).
Congressional Research Service
4
California and the Clean Air Act (CAA) Waiver: Frequently Asked Questions
Only California can qualify for such a preemption waiver because it is the only state that adopted
new motor vehicle emissions standards “prior to March 30, 1966.”26
EPA is to grant the waiver absent certain disqualifying conditions. CAA Section 209(b) lists three
conditions under which EPA may determine that California does not qualify for a preemption
waiver:
1. the determination of the State is arbitrary and capricious,
2. such State does not need such State standards to meet compelling and
extraordinary conditions, or
3. such State standards and accompanying enforcement procedures are not
consistent with Section 202(a) of the CAA.27
If the EPA administrator determines that any of these three conditions are not met, the statute
requires that the administrator deny California’s request for a waiver.
Preemption of State Emissions Standards for New Nonroad
Vehicles or New Nonroad Vehicle Engines
The CAA Amendments of 1990 (P.L. 101-549) added Section 209(e),28 which provides for a
similar scheme of federal preemption to allow California to seek EPA authorization to adopt and
enforce emissions standards for some new nonroad vehicles and new nonroad vehicle engines.29
To be granted authorization, California’s regulations must conform to the same requirements for
new motor vehicles and new motor vehicle engines in Section 209(b) discussed above.
CAA Section 209(e)(1) prohibits all states, including California, from adopting or enforcing air
pollutant emissions standards for two specific classes of new nonroad vehicles or new nonroad
vehicle engines. These preempted classes are
1. new engines which are used in construction equipment or vehicles or used in
farm equipment or vehicles and which are smaller than 175 horsepower, and
2. new locomotives or new engines used in locomotives.30
CAA Section 209(e)(2) provides an authorization for California to adopt and enforce standards
and other requirements relating to the control of emissions from all other classes of new nonroad
vehicles and engines under conditions similar to those in Section 209(b).31
California’s Waivers and Authorizations
According to EPA records, since 1967, CARB has submitted more than 100 waiver requests
under Section 209(b) or authorization requests under Section 209(e) for new or amended statelevel vehicle emissions standards or “within the scope” determinations (i.e., a request that EPA
26 S. Rept. 403, 90th Cong., 1st sess., 1967.
27 42 U.S.C. §7543(b)(1).
28 42 U.S.C. §7543(e).
29 The term nonroad vehicle means “a vehicle that is powered by a nonroad engine and that is not a motor vehicle or a
vehicle used solely for competition.” 42 U.S.C. §7550(11). The term nonroad engine means “an internal combustion
engine (including the fuel system) that is not used in a motor vehicle or a vehicle used solely for competition, or that is
not subject to standards promulgated under section 7411 of this title or section 7521 of this title.” 42 U.S.C. §7550(10).
30 42 U.S.C. §7543(e)(1).
31 42 U.S.C. §7543(e)(2).
Congressional Research Service
5
California and the Clean Air Act (CAA) Waiver: Frequently Asked Questions
rule on whether a new state regulation is within the scope of a waiver or authorization that EPA
has already issued).32 The waivers and authorizations cover California regulations for light-duty
vehicles, heavy-duty vehicles, buses, motorcycles, off-highway recreational vehicles, small offroad engines, in-use locomotives, commercial harbor craft, personal watercraft, ocean-going
vessels, at-berth shore power, zero-emission vehicles, portable diesel equipment, evaporative
emissions, refueling vapor recovery, idling requirements, onboard diagnostics, warranty
programs, label specifications, assembly-line test procedures, nonroad durability requirements,
defect reporting, in-use recall, in-use enforcement testing, and certification fees, among others.
Since 1967, EPA has granted waivers, authorizations, and “within the scope” determinations for
all but one of California’s requests. The sole denial, in 2008, was for California’s initial waiver
request for its MY2009 light-duty vehicle GHG emissions standards.33 The sole withdrawal of a
granted waiver, in 2019, was for California’s waiver for its light-duty vehicle GHG standards
applicable to MY2021-MY2025.
What Is the Process by Which California Applies for
a Waiver?
CAA Section 209(b) allows California to seek a waiver from the federal preemption provision
that prohibits states from enacting emissions standards for new motor vehicles or new motor
vehicle engines.34 In such a circumstance, EPA must grant a waiver before California’s rules may
be enforced. When California files a waiver request, EPA publishes a notice for public hearing
and written comment regarding California’s request in the Federal Register. The written
comment period remains open for a period of time after the public hearing. Once the comment
period expires, EPA reviews the comments, and the EPA administrator determines whether the
requirements for obtaining a waiver as provided under CAA Section 209(b) have been met. EPA
publishes its determination in the Federal Register.
Further, CAA Section 209(e) allows California to seek authorization to enforce its own standards
for certain new nonroad vehicles and new nonroad vehicle engines, despite the preemption
provision that prohibits states from enacting emissions standards for such vehicles.35 When
California files an authorization request, EPA publishes a notice for public hearing and written
comment regarding California’s request in the Federal Register. The written comment period
remains open for a period of time after the public hearing. Once the comment period expires, EPA
reviews the comments, and the EPA administrator determines whether the requirements for
obtaining an authorization as provided under CAA Section 209(e) have been met. EPA publishes
the authorization in the Federal Register.
32 EPA, “Vehicle Emissions California Waivers and Authorizations,” https://www.epa.gov/state-and-local-
transportation/vehicle-emissions-california-waivers-and-authorizations#state (listing Federal Register notices of waiver
requests and decisions); Letter from Kevin de Leon, President pro Tempore, California Senate, et al. to Xavier Becerra,
Attorney General, California Department of Justice, March 16, 2017.
33 EPA, “California State Motor Vehicle Pollution Control Standards; Notice of Decision Denying a Waiver of Clean
Air Act Preemption for California’s 2009 and Subsequent Model Year Greenhouse Gas Emissions,” 73 Federal
Register 12156, March 6, 2008. For more on this denial and the subsequent actions, see the section “What Is the
History of California’s Clean Air Act Waivers for Motor Vehicle GHG Emissions?” in this report.
34 42 U.S.C. §7543(b).
35 42 U.S.C. §7543(e).
Congressional Research Service
6
California and the Clean Air Act (CAA) Waiver: Frequently Asked Questions
How Can Other States Adopt California’s Vehicle
Standards?
Under certain conditions, other states can adopt California’s vehicle emissions standards through
provisions in CAA Sections 177 and 209(e).36
The federal preemptions in CAA Sections 209(a) and 209(e) provide automakers some level of
nationwide regulatory certainty and a remit from the possibility of a “patchwork quilt” of
numerous and differing state-level regulatory programs for emissions from new vehicles or
engines. However, some states with air pollution control issues (e.g., those with CAA State
Implementation Plans for one or more criteria pollutants under the CAA’s National Ambient Air
Quality Standards37) have looked for ways to reduce air pollution from the mobile source sector,
including the possibility of greater reductions from new vehicles or engines.
To this end, the CAA Amendments of 1990 (P.L. 101-549) included provisions to allow other
states to adopt California’s emissions standards for new motor vehicles or new motor vehicle
engines under certain conditions.38 CAA Section 177 requires that the state must have an EPAapproved State Implementation Plan, that the standards adopted by the state be identical to the
California standards for which a waiver or authorization has been granted, and that adoption of
such standards provide at least a two-year manufacturer lead time. States are not required to seek
EPA approval under the terms of Section 177.39
As of this writing, 17 states and the District of Columbia have adopted some subset of
California’s motor vehicle air pollutant and GHG emissions standards under these provisions (see
Figure 1).40 CARB estimates that California and the “Section 177 States” accounted for 39.7% of
new light-duty vehicle registrations and 25.4% of new heavy-duty vehicle registrations.41
For new nonroad vehicles and new nonroad vehicle engines, CAA Section 209(e)(2) includes a
provision that permits other states to adopt the standards for which California has received EPA
authorization, similar to the provisions for new motor vehicles and new motor engines in Section
177.42 States can adopt such standards so long as the standards are identical to those adopted by
36 42 U.S.C. §7507; 42 U.S.C. §7543(e)(2)(B).
37 The CAA requires EPA to set National Ambient Air Quality Standards (NAAQS) for six commonly found air
pollutants known as criteria air pollutants. For a discussion of Clean Air Act National Ambient Air Quality Standards
and State Implementation Plans, see CRS Report RL30853, Clean Air Act: A Summary of the Act and Its Major
Requirements, by Richard K. Lattanzio (2022).
38 42 U.S.C. §7507.
39 Similar requirements for new nonroad vehicles and engines are included under 42 U.S.C. §7543(e)(2)(b).
40 The Section 177 states are Colorado, Connecticut, Delaware, Maine, Maryland, Massachusetts, Minnesota, Nevada,
New Jersey, New Mexico, New York, Oregon, Pennsylvania, Rhode Island, Vermont, Virginia, Washington, and the
District of Columbia.
41 California Air Resources Board (CARB), “Section 177 States Regulation Dashboard,” https://ww2.arb.ca.gov/ourwork/programs/advanced-clean-cars-program/states-have-adopted-californias-vehicle-regulations. CARB calculates the
percentages for state share of U.S. light-duty vehicle registrations using data from the National Automobile Dealers
Association (NADA) report NADA Data 2023 Annual Financial Profile of America’s Franchised New-Car
Dealerships. CARB calculates the percentages for state share of U.S. heavy-duty vehicles registered using “Trucks”
and “Buses” data from the Federal Highway Administration (FHWA) report State Motor-Vehicle Registrations – 2022,
Table MV-1.
42 42 U.S.C. §7543(e)(2)(B). In order for a state to be eligible to adopt California standards, the state must have an
EPA-approved State Implementation Plan.
Congressional Research Service
7
California and the Clean Air Act (CAA) Waiver: Frequently Asked Questions
California and California and the state provide at least two years before the standard takes
effect.43
Figure 1. States That Have Adopted a Selection of California’s Motor Vehicle
Standards
Source: CRS, with data from California Air Resources Board, “States That Have Adopted California’s Vehicle
Regulations,” https://ww2.arb.ca.gov/our-work/programs/advanced-clean-cars-program/states-have-adoptedcalifornias-vehicle-regulations, as of April 2025.
Notes: The California standards in the figure are noncomprehensive. They represent the seven light- and heavyduty motor vehicle emissions standards that date from 1990 and include Advanced Clean Cars II, Low Emission
Vehicle Criteria Pollutant, Low Emission Vehicle Greenhouse Gas, Zero-Emission Vehicle, Advanced Clean
Trucks, Heavy-Duty Omnibus, Heavy-Duty Phase 2 Greenhouse Gas. The years by which each state adopted (or
is scheduled to adopt) the respective standards are listed on CARB’s website. Debate exists on the legal status
of adoption of certain standards in some states (e.g., Virginia).
43 Ibid. §7543(e)(2)(B)(i), (ii). In the Consolidated Appropriations Act of 2004, Congress prohibited states other than
California from adopting emissions standards for “spark ignition engines” smaller than 50 horsepower. P.L. 108-199
§428(c), (d), 118 Stat. 418 (2004). The act included a provision that grandfathered any state standards that were
adopted before September 1, 2003. Ibid. §428(e), 118 Stat. 419. EPA has adopted regulations implementing these
provisions. 40 C.F.R. §1074.110(b).
Congressional Research Service
8
California and the Clean Air Act (CAA) Waiver: Frequently Asked Questions
What is the Status of California’s Waiver Requests?
As of April 2025, there are no waiver or authorization requests from California for vehicle
emissions standards pending EPA action.44
Between December 2024 and April 2025, EPA and CARB acted on a number of waiver and
authorization requests. In particular, EPA granted certain waiver and authorization requests, in
their entirety or in part, while CARB withdrew others, in their entirety or in part.
EPA granted waivers or authorization requests for the following regulations:
•
•
•
•
Advanced Clean Cars II (ACC II),45
Heavy-Duty Omnibus Low NOX,46
Small Off-Road Engines (SORE),47 and
In-Use Off-Road Diesel-Fueled Fleets.48
EPA granted partial authorizations for the following regulations—approving some elements while
taking no action on others:49
•
•
Commercial Harbor Craft,50 and
Transport Refrigeration Unit (TRU).51
CARB withdrew its requests for a waiver or authorization for the following regulations:
•
•
Advanced Clean Fleets,52 and
In-Use Locomotive.53
44 EPA, “Vehicle Emissions California Waivers and Authorizations,” https://www.epa.gov/state-and-local-
transportation/vehicle-emissions-california-waivers-and-authorizations, archived April 3, 2025, at
https://perma.cc/CM7Q-TEEL.
45 EPA, “California State Motor Vehicle and Engine Pollution Control Standards; Advanced Clean Cars II; Waiver of
Preemption; Notice of Decision,” 90 Federal Register 642, January 6, 2025.
46 EPA, “California State Motor Vehicle and Engine and Nonroad Engine Pollution Control Standards; The
‘‘Omnibus’’ Low NOX Regulation; Waiver of Preemption; Notice of Decision,” 90 Federal Register 643, January 6,
2025.
47 EPA, “California State Nonroad Engine Pollution Control Standards; Small Off-Road Engines Regulations; Notice
of Decision,” 90 Federal Register 640, January 6, 2025.
48 EPA, “California State Nonroad Engine Pollution Control Standards; In-Use Off-Road Diesel Fueled Fleets; Notice
of Decision,” 90 Federal Register 1996, January 10, 2025.
49 CARB subsequently withdrew its requests for the elements on which EPA did not act. For information about the
requirements for which CARB withdrew its authorization request, see Letter from Steven Cliff, Executive Office, to
Jane Nishida, Acting EPA Administrator, 2025, https://www.epa.gov/system/files/documents/2025-01/ca-chc-carbwithdrawal-ltr-2025-1-13.pdf.
50 For the authorization EPA granted, see EPA “California State Nonroad Engine Pollution Control Standards;
Commercial Harbor Craft Regulations; Notice of Decision,” 90 Federal Register 1998, January 10, 2025.
51 For the authorization EPA granted, see EPA, “California State Nonroad Engine Pollution Control Standards; In-Use
Diesel-Fueled Transport Refrigeration Units (TRU) and TRU Generator Sets; Notice of Decision,” 90 Federal Register
2000, January 10, 2025.
52 Letter from Jane Nishida, Acting EPA Administrator, to Steven Cliff, Executive Officer, 2025,
https://www.epa.gov/system/files/documents/2025-01/hd-acf-carb-waiver-withdraw-resp-2025-1-14.pdf.
53 Letter from Jane Nishida, Acting EPA Administrator, to Steven Cliff, Executive Officer, 2025,
https://www.epa.gov/system/files/documents/2025-01/loco-carb-waiver-withdraw-resp-2025-1-14.pdf.
Congressional Research Service
9
California and the Clean Air Act (CAA) Waiver: Frequently Asked Questions
At the time of this report, three joint resolutions of disapproval have been introduced in each
chamber of 119th Congress concerning EPA waivers. The joint resolutions concern EPA’s waivers
for the ACC II, the Heavy-Duty Omnibus Low NOX, and the Advanced Clean Trucks regulation,
respectively (see “Can Clean Air Act Waivers Be Reviewed Under the Congressional Review
Act?”).54 On April 30, 2025, the House voted to adopt its versions of the joint resolutions
(H.J.Res 88, H.J.Res 89, and H.J.Res 87).55
Heavy-Duty Omnibus Low NOX Waiver Request
On January 31, 2022, CARB submitted a request that EPA grant a waiver of preemption and an
authorization under the CAA for a regulation that would establish criteria pollutant exhaust
emissions standards for new MY2024 and subsequent model year on-road medium- and heavyduty engines and vehicles. The regulation would also establish emissions-related requirements for
some off-road engines.56
On January 6, 2025, EPA issued a notice of decision granting CARB’s request for a waiver of
CAA preemption for its Heavy-Duty Vehicle and Engine “Omnibus” Low NOX regulation.57
EPA’s decision also includes an authorization for portions of the Omnibus Low NOX program that
pertain to off-road engines.
Small Off-Road Engine (SORE) Authorization Request
On December 20, 2022, CARB submitted a new authorization request to EPA for its 2016 and
2021 amendments to its Small Off-Road Engine (SORE) regulations. The 2016 SORE
Amendments would include improvements to evaporative emissions certification procedures,
revisions to the compliance testing procedure, and updates to the evaporative emissions
certification test fuel. The 2021 SORE Amendments would establish exhaust and evaporative
emissions standards and associated test procedures for MY2024 and subsequent model engines
and equipment that would be significantly more stringent than existing procedures.58
On January 6, 2025, EPA issued a notice of decision granting CARB’s request for an
authorization to its SORE regulations.59
54 EPA, “California State Motor Vehicle and Engine Pollution Control Standards; Heavy-Duty Vehicle and Engine
Emission Warranty and Maintenance Provisions; Advanced Clean Trucks; Zero Emission Airport Shuttle; ZeroEmission Power Train Certification; Waiver of Preemption; Notice of Decision,” 88 Federal Register 20688, April 6,
2023.
55 H.J. Res 87, 88, 89; S.J. Res. 45, 46, 47.
56 EPA, “California State Motor Vehicle Pollution Control Standards and Nonroad Engine Pollution Control Standards;
The ‘Omnibus’ Low NOX Regulation; Request for Waivers of Preemption; Opportunity for Public Hearing and Public
Comment,” 87 Federal Register 35765, June 13, 2022. For more information about the Heavy-Duty Omnibus Low
NOX regulation, see CARB, “Heavy-Duty Low NOX,” https://ww2.arb.ca.gov/our-work/programs/heavy-duty-low-nox,
accessed April 25, 2025.
57 EPA, “California State Motor Vehicle and Engine and Nonroad Engine Pollution Control Standards; The
‘‘Omnibus’’ Low NOX Regulation; Waiver of Preemption; Notice of Decision,” 90 Federal Register 643, January 6,
2025.
58 EPA, “California State Nonroad Engine Pollution Control Standards; Small Off-Road Engines; Requests for
Authorization; Opportunity for Public Hearing and Comment,” 88 Federal Register 33143, May 23, 2023. For more
information about the Small Off-Road Engine regulations and amendments, see CARB, “Small Off-Road Engines
(SORE),” https://ww2.arb.ca.gov/our-work/programs/small-off-road-engines-sore, accessed April 25, 2025.
59 EPA, “California State Nonroad Engine Pollution Control Standards; Small Off-Road Engines Regulations; Notice
of Decision,” 90 Federal Register 640, January 6, 2025.
Congressional Research Service
10
California and the Clean Air Act (CAA) Waiver: Frequently Asked Questions
Transport Refrigeration Unit Authorization Request
On December 29, 2022, CARB submitted a new authorization request to EPA for its amendments
to its In-Use Diesel-Fueled Transport Refrigeration Units and Generator Sets (collectively,
‘‘TRU’’) regulations. These would include, among other provisions, a requirement that certain
TRUs manufactured after a certain date use a refrigerant less than or equal to a specified global
warming potential (GWP), a requirement that nontruck TRUs meet specified particulate matter
(PM) standards, a requirement that TRU owners transition a percentage of their truck fleet TRUs
to zero-emission technology, and a requirement that owners of certain facilities be subject to
registration and reporting requirements.60
On January 10, 2025, EPA issued a notice of decision granting partial authorization of its TRU
regulations.61
On January 13, 2025, CARB withdrew its request for authorization for requirements within the
2022 TRU Amendments on which EPA did not issue a determination. These included the
provisions requiring the turnover of at least 15% of the diesel-fueled TRU to zero-emission TRU
by December 31, 2023, and each year thereafter.62
Commercial Harbor Craft Authorization Request
On January 31, 2023, CARB submitted a new authorization request to EPA concerning
amendments to the Commercial Harbor Craft regulation.63 The 2022 Commercial Harbor Craft
Amendments revise the emission standards and other emissions-related requirements applicable
to both new and in-use diesel propulsion and auxiliary engines on commercial harbor craft that
operate within regulated California waters. The amendments also extend the requirements to
additional categories of commercial harbor craft: pilot boats, push boats, workboats, research
vessels, commercial passenger fishing vessels, commercial fishing vessels, and temporary
replacement vessels, as well as tank barges under 400 feet and 10,000 gross tons. The 2022
Commercial Harbor Craft Amendments create new emission standards and compliance dates that
are different depending on vessel category and, for existing vessels, engine model year. The
amendments include Zero-Emission and Advanced Technologies (ZEAT) requirements for new
and in-use ferries and new excursion vessels that began phasing in on December 31, 2024.
On January 10, 2025, EPA issued a notice of decision granting a partial authorization for CARB’s
2022 Commercial Harbor Craft Amendments except for certain provisions on which EPA
announced it was not taking action at that time: (1) provisions related to the ZEAT standards for
in-use short run ferries; and (2) provisions related to standards for in-use engines and vessels
(excluding commercial fishing vessels) that would apply after the expiration of the feasibility
EPA, “California State Nonroad Engine Pollution Control Standards; In-Use Diesel-Fueled Transport Refrigeration
Units (TRU) and TRU Generator Sets and In-Use Off-Road Diesel Fueled Fleets; Requests for Authorization;
Opportunity for Public Hearing and Comment,” 89 Federal Register 32422, April 26, 2024. For more information
about the TRU regulations, see CARB, “Transport Refrigeration Unit,” https://ww2.arb.ca.gov/ourwork/programs/transport-refrigeration-unit, accessed April 25, 2025.
61 EPA, “California State Nonroad Engine Pollution Control Standards; In-Use Diesel-Fueled Transport Refrigeration
Units (TRU) and TRU Generator Sets; Notice of Decision,” 90 Federal Register 2000, January 10, 2025.
62 Letter from Steven Cliff, Executive Office, to Jane Nishida, Acting EPA Administrator, 2025,
https://www.epa.gov/system/files/documents/2025-01/ca-tru-carb-withdrawal-ltr-2025-1-13.pdf.
63 EPA, “California State Nonroad Engine Pollution Control Standards; Commercial Harbor Craft; Notice of Public
Hearing,” 81 Federal Register 25636, January 27, 2023.
60
Congressional Research Service
11
California and the Clean Air Act (CAA) Waiver: Frequently Asked Questions
extensions when an engine or diesel particulate filter is not feasible and the owner cannot afford
vessel replacement.64
On January 13, 2025, CARB withdrew its request for authorization for the two elements of the
2022 Commercial Harbor Craft Amendments on which EPA had not taken action as noted
above.65
Advanced Clean Cars II Waiver Request
On May 22, 2023, CARB submitted a request that EPA grant a waiver of preemption under the
CAA for its Advanced Clean Cars II regulation (ACC II). The regulation would establish criteria
and GHG pollutant emissions standards for new MY2026 and subsequent model year California
on-road light- and medium-duty vehicles. The regulation would include two sets of requirements,
one for conventional vehicles powered by internal combustion engines and one for zero-emission
vehicles (with plug-in hybrid electric vehicles subject to both sets).66 On January 6, 2025, EPA
issued a notice of decision granting CARB’s request for a waiver of CAA preemption for its ACC
II regulation.67
In-Use Off-Road Diesel-Fueled Fleets Authorization Request
On November 2, 2023, CARB submitted a new authorization request to EPA for its amendments
to its In-Use Off-Road Diesel-Fueled Fleets regulation. The amendments require fleets of in-use
off-road diesel-fueled vehicles to phase out the operation of their oldest and highest-emitting
diesel vehicles and would prohibit such fleets from acquiring high-emitting vehicles. The
regulation would also require fleets to fuel their vehicles with specified renewable diesel.68 On
January 10, 2024, EPA issued a notice of decision granting CARB’s request for an authorization
for its In-Use Off-Road Diesel-Fueled Fleets amendments.69
In-Use Locomotive Authorization Request
On November 7, 2023, CARB submitted a new authorization request to EPA for its In-Use
Locomotive regulation. The regulation contains several provisions that would apply to any
locomotive operator that operates a locomotive in the State of California. The regulation would
64 EPA, “California State Nonroad Engine Pollution Control Standards; Commercial Harbor Craft Regulations; Notice
of Decision,” 90 Federal Register 1998, January 10, 2025.
65 Letter from Steven Cliff, Executive Office, to Jane Nishida, Acting EPA Administrator, 2025,
https://www.epa.gov/system/files/documents/2025-01/ca-chc-carb-withdrawal-ltr-2025-1-13.pdf.
66 EPA, “California State Motor Vehicle Pollution Control Standards; Advanced Clean Cars II Regulations; Request for
Waiver of Preemption; Opportunity for Public Hearing and Public Comment,” 88 Federal Register 88908, December
26, 2023. For more information about the Advanced Clean Cars II regulation, see CARB, “Advanced Clean Cars II,”
https://ww2.arb.ca.gov/our-work/programs/advanced-clean-cars-program/advanced-clean-cars-ii, accessed April 25,
2025.
67 EPA, “California State Motor Vehicle and Engine Pollution Control Standards; Advanced Clean Cars II; Waiver of
Preemption; Notice of Decision,” 90 Federal Register 642, January 6, 2025.
68 EPA, “California State Nonroad Engine Pollution Control Standards; In-Use Diesel-Fueled Transport Refrigeration
Units (TRU) and TRU Generator Sets and In-Use Off-Road Diesel Fueled Fleets; Requests for Authorization;
Opportunity for Public Hearing and Comment,” 89 Federal Register 32433, April 26, 2024. For more information
about CARB’s In-Use Off-Road Diesel-Fueled Fleet regulation and amendments, see CARB, “In-Use Off-Road
Diesel-Fueled Fleets Regulation,” https://ww2.arb.ca.gov/our-work/programs/use-road-diesel-fueled-fleets-regulation,
accessed April 25, 2025.
69 EPA, “California State Nonroad Engine Pollution Control Standards; In-Use Off-Road Diesel Fueled Fleets; Notice
of Decision,” 90 Federal Register 1996. January 10, 2025.
Congressional Research Service
12
California and the Clean Air Act (CAA) Waiver: Frequently Asked Questions
include a ‘‘Spending Account’’ provision and an ‘‘In-Use Locomotive Operational Requirement,’’
which, according to CARB, would start January 1, 2030, and would allow only locomotives with
an original engine build date less than 23 years old to operate in California, with some exceptions.
Further, the regulation would include an idling requirement in the form of a 30-minute Automatic
Engine Stop Start (AESS) and would impose registration, reporting, and recordkeeping
requirements on locomotive operators for all activity in California.70 On January 13, 2025, CARB
withdrew its request for authorization for its In-Use Locomotive regulation.71
Advanced Clean Fleets Waiver Request
On November 15, 2023, CARB submitted a request that EPA grant a waiver of preemption and an
authorization under the CAA for CARB’s Advanced Clean Fleets regulation. The regulation
would require affected state and local government fleets, drayage truck fleets, federal government
agency fleets, and large commercial fleets to incorporate zero-emitting on-road medium and
heavy-duty vehicles and light-duty package delivery vehicles into their fleets, beginning in
MY2024. The regulation would additionally require that all new California medium- and heavyduty vehicles sold be zero-emitting vehicles starting in MY2036.72
On January 13, 2025, CARB withdrew its request for a waiver of CAA preemption for its
Advanced Clean Fleets regulation.73
Advanced Clean Trucks
On December 20, 2021, CARB submitted a request that EPA grant a waiver of preemption under
the CAA for CARB’s Advanced Clean Trucks Regulation. The regulation requires that
manufacturers produce and sell increasing quantities of medium- and heavy-duty zero-emission
vehicles and near-zero-emission vehicles in California, starting with the 2024 model year through
2035, by which point zero-emission vehicle sales must make up 40% to 75% of new truck sales,
depending on the vehicle class.74
On April 6, 2023, EPA issued a notice of decision granting CARB’s request for a waiver of CAA
preemption for its Advanced Clean Trucks regulation.75
70 EPA, “California State Nonroad Engine Pollution Control Standards; In-Use Locomotive Regulation; Requests for
Authorization; Opportunity for Public Hearing and Comment,” 89 Federal Register 14484, February 27, 2024. For
more information about the In-Use Locomotive regulation, see CARB, “Reducing Rail Emissions in California,”
https://ww2.arb.ca.gov/our-work/programs/reducing-rail-emissions-california, accessed April 25, 2025.
71 Letter from Jane Nishida, Acting EPA Administrator, to Steven Cliff, Executive Officer, 2025,
https://www.epa.gov/system/files/documents/2025-01/loco-carb-waiver-withdraw-resp-2025-1-14.pdf.
72 EPA, “California State Motor Vehicle Pollution Control Standards; Advanced Clean Fleets Regulation; Request for
Waiver of Preemption and Authorization; Opportunity for Public Hearing and Public Comment,” 89 Federal Register
57151, July 12, 2024. For more information about the Advanced Clean Fleets Regulation, see CARB, “Advanced
Clean Fleets,” https://ww2.arb.ca.gov/our-work/programs/advanced-clean-fleets, accessed April 25, 2025.
73 Letter from Jane Nishida, Acting EPA Administrator, to Steven Cliff, Executive Officer, 2025,
https://www.epa.gov/system/files/documents/2025-01/hd-acf-carb-waiver-withdraw-resp-2025-1-14.pdf.
74 EPA, “California State Motor Vehicle Pollution Control Standards; Advanced Clean Trucks; Zero Emission Airport
Shuttle; Zero-Emission Power Train Certification; Request for Waiver of Preemption; Opportunity for Public Hearing
and Public Comment,” 87 Federal Register 113, June 13, 2022. For more information about CARB’s Advanced Clean
Trucks Rule, see CARB, “Advanced Clean Trucks,” https://ww2.arb.ca.gov/our-work/programs/advanced-clean-trucks,
accessed April 25, 2025.
75 EPA, “California State Motor Vehicle and Engine Pollution Control Standards; Heavy-Duty Vehicle and Engine
Emission Warranty and Maintenance Provisions; Advanced Clean Trucks; Zero Emission Airport Shuttle; Zero(continued...)
Congressional Research Service
13
California and the Clean Air Act (CAA) Waiver: Frequently Asked Questions
What Is the History of California’s Clean Air Act
Waivers for Motor Vehicle GHG Emissions?
Although EPA has granted California more than 100 waivers across multiple administrations for
various mobile source emissions standards, waivers for California’s GHG emissions standards
have been far more controversial. Since the early 2000s, changes in presidential administration
often have led to changes in EPA’s approach to granting waivers for GHG emissions standards.
The following section summarizes the differing approaches taken by each administration starting
with that of President George W. Bush.
Actions Under the Bush Administration
In July 2002, California became the first state to enact legislation requiring reductions of GHG
emissions from new motor vehicles. The legislation, AB 1493, required CARB to adopt
regulations requiring the “maximum feasible and cost-effective reduction” of GHG emissions
from any vehicle whose primary use is noncommercial personal transportation.76 The reductions
applied to new MY2009 motor vehicles and subsequent model years. Under this authority, CARB
adopted regulations in September 2004, and submitted a request to EPA in December 2005, for a
federal preemption waiver.
In 2008, EPA denied California’s request for a waiver.77 As it explained in its decision, EPA
concluded that “California does not need its GHG standards for new motor vehicles to meet
compelling and extraordinary conditions” because “the atmospheric concentrations of these
greenhouse gases is [sic] basically uniform across the globe” and are not uniquely connected to
California’s “peculiar local conditions.”78
Actions Under the Obama Administration
In 2009, EPA reconsidered and reversed its prior waiver denial, granting the waiver for
California’s MY2009 and subsequent model year GHG emissions standards.79 In reversing its
denial, EPA determined that the “better approach” is for the agency to evaluate whether California
“needs” state standards “to meet compelling and extraordinary conditions” based on California’s
need for its motor vehicle program as a whole, not solely based on GHG standards addressed in
the waiver request.80 Under this approach, EPA concluded that it cannot deny the waiver request
because California has “repeatedly” demonstrated the need for its motor vehicle program to
address “serious” local and regional air pollution problems.81
Emission Power Train Certification; Waiver of Preemption; Notice of Decision,” 88 Federal Register 20688, April 6,
2023.
76 Ch. 200, Sec. 3(a), Cal. Stats. Regular Session, 2002, p. 867 (codified at Cal. Health and Safety Code §43018.5),
https://clerk.assembly.ca.gov/sites/clerk.assembly.ca.gov/files/archive/Statutes/2002/2002_Statutes_1667_Vol_1.pdf.
77 EPA, “California State Motor Vehicle Pollution Control Standards; Notice of Decision Denying a Waiver of Clean
Air Act Preemption for California’s 2009 and Subsequent Model Year Greenhouse Gas Emissions,” 73 Federal
Register 12156, March 6, 2008.
78 Ibid., pp. 12159-12169.
79 EPA, “California State Motor Vehicle Pollution Control Standards; Notice of Decision Granting a Waiver of Clean
Air Act Preemption for California’s 2009 and Subsequent Model Year Greenhouse Gas Emission Standards for New
Motor Vehicles,” 74 Federal Register 32744, July 8, 2009.
80 Ibid., pp. 32761-32763.
81 Ibid., pp. 32762-32763.
Congressional Research Service
14
California and the Clean Air Act (CAA) Waiver: Frequently Asked Questions
Upon receiving the 2009 waiver, CARB joined EPA and the National Highway Traffic Safety
Administration (NHTSA, which administers the Corporate Average Fuel Economy [CAFE]
program)82 to develop the National Program. The National Program was designed to align federal
fuel economy standards, federal GHG emissions standards, and California’s adopted GHG
emissions standards under one rubric such that the regulated entities (i.e., the automakers) would
be able to produce a single fleet of motor vehicles that could comply with all three regulatory
programs.
Three key provisions of the 2009 agreement between the Obama Administration, the automakers,
and the State of California were that (1) EPA would grant California a waiver for its MY2017MY2025 standards known as Advanced Clean Cars (ACC) I (the agency did so in January
2013);83 (2) California would accept vehicles complying with the federal greenhouse standards as
meeting the California standards;84 and (3) the automakers would drop their outstanding suit
challenging the California standards.
Shortly after the 2009 agreement, EPA and NHTSA engaged in a series of rulemakings that set
out increasingly stringent GHG and fuel economy standards. It was these standards that
California agreed to deem compliant with its ACC I standards for which it was granted a waiver
in 2013. EPA and NHTSA promulgated a joint rulemaking affecting MY2012-MY2016 light-duty
vehicles in May 2010. This was known as the Phase 1 standards.85
The agencies promulgated a second phase of CAFE and GHG emissions standards affecting
MY2017-MY2025 light-duty vehicles in October 2012.86 As part of the Phase 2 rulemaking, EPA
and NHTSA made a commitment to conduct a midterm evaluation (MTE) for the latter half of the
standards, MY2022-MY2025.87 Through the MTE, the EPA administrator was to determine
whether EPA’s standards for MY2022-MY2025 were still appropriate given the latest available
data and information.88
In November 2016, EPA released a proposed determination stating that the MY2022-MY2025
standards remained appropriate and that a rulemaking to change them was not warranted.89 In
January 2017, during the final days of the Obama Administration, then-EPA Administrator Gina
82 NHTSA derives its authority to regulate the fuel economy of motor vehicles from the Energy Policy and
Conservation Act of 1975 (EPCA; P.L. 94-163) as amended by the Energy Independence and Security Act of 2007
(EISA; P.L. 110-140), as codified at 49 U.S.C. §§32901-32919.
83 EPA, “California State Motor Vehicle Pollution Control Standards; Notice of Decision Granting a Waiver of Clean
Air Act Preemption for California’s Advanced Clean Car Program and a Within the Scope Confirmation for
California’s Zero Emission Vehicle Amendments for 2017 and Earlier Model Years,” 78 Federal Register 2112,
January 9, 2013 (hereinafter 78 Federal Register 2112).
84 Letter from Mary D. Nichols, Chairman, CARB, to Ray LaHood, Secretary, U.S. Department of Transportation, and
Lisa Jackson, Administrator, Environmental Protection Agency, July 28, 2011, https://www.epa.gov/sites/production/
files/2016-10/documents/carb-commitment-ltr.pdf. The condition set forth by CARB was that the “deemed to comply”
provision was contingent upon EPA adopting “a final rule that at a minimum preserves the greenhouse reduction
benefits set forth in U.S. EPA’s December 1, 2011 Notice of Proposed Rulemaking for 2017 through 2025 model year
passenger vehicles.” CARB Resolution 12-11, January 26, 2012, p. 20.
85 EPA, “Light-Duty Vehicle Greenhouse Gas Emission Standards and Corporate Average Fuel Economy Standards;
Final Rule,” 75 Federal Register 25324, May 7, 2010.
86 EPA and NHTSA, “2017 and Later Model Year Light-Duty Vehicle Greenhouse Gas Emissions and Corporate
Average Fuel Economy Standards; Final Rule,” 77 Federal Register 62624, October 15, 2012.
87 Ibid., p. 62652.
88 The rulemaking specified EPA as the agency to determine whether the standards established for MY2022-MY2025
are appropriate. See ibid.
89 EPA, “Proposed Determination on the Appropriateness of the Model Year 2022-2025 Light-Duty Vehicle
Greenhouse Gas Emissions Standards Under the Midterm Evaluation,” 81 Federal Register 87928, December 6, 2016.
Congressional Research Service
15
California and the Clean Air Act (CAA) Waiver: Frequently Asked Questions
McCarthy finalized the determination and stated that “the standards adopted in 2012 by the EPA
remained feasible, practical and appropriate.”90
Actions Under the First Trump Administration
In March 2017, EPA and NHTSA announced their joint intention to reconsider the Obama
Administration’s final determination and reopen the MTE process.91 In April 2018, EPA released
a revised final determination, stating that the MY2022-MY2025 standards were “not appropriate
and, therefore, should be revised.”92 The notice stated that the January 2017 final determination
was based on “outdated information, and that more recent information suggested that the current
standards were too stringent.”93
In August 2018, EPA and NHTSA proposed amendments to the existing CAFE and GHG
emissions standards, the Safer Affordable Fuel-Efficient Vehicles Rule for Model Years 20212026 Passenger Cars and Light Trucks (SAFE Vehicles Rule).94 Further, EPA proposed to
withdraw California’s CAA preemption waiver for its vehicle GHG standards applicable to
MY2021-MY2025.95 Separately, NHTSA contended that the Energy Policy and Conservation Act
of 1975, as amended (EPCA; P.L. 94-163; the statutory basis for the CAFE standards), preempts
California’s standards because the statute preempts state laws related to federal fuel economy
standards.96
NHTSA’s Interpretation of EPCA Preemption
In September 2019, EPA and NHTSA finalized the Safer, Affordable, Fuel-Efficient (SAFE)
Vehicles Rule, Part One: One National Program (SAFE rule or Part One rule).97 In the Part One
rule, NHTSA asserted its statutory authority to set nationally applicable fuel economy standards
under EPCA. At the time, NHTSA interpreted EPCA as preempting state and local GHG
standards because such standards are “related to” fuel economy standards.98 The principle that
90 EPA, “Final Determination on the Appropriateness of the Model Year 2022-2025 Light-Duty Vehicle Greenhouse
Gas Emissions Standards Under the Midterm Evaluation,” EPA-420-R-17-001, January 2017, https://nepis.epa.gov/
Exe/ZyPURL.cgi?Dockey=P100QQ91.txt.
91 EPA, “News Release: EPA to Reexamine Emission Standards for Cars and Light-Duty Trucks—Model Years 20222025,” March 15, 2017, https://www.epa.gov/archive/epa/newsreleases/epa-reexamine-emission-standards-cars-andlight-duty-trucks-model-years-2022-2025.html.
92 EPA, “Mid-Term Evaluation of Greenhouse Gas Emissions Standards for Model Year 2022-2025 Light-Duty
Vehicles: Notice; Withdrawal,” 83 Federal Register 16077, April 13, 2018.
93 Ibid.
94 EPA and NHTSA, “The Safer, Affordable, Fuel-Efficient (SAFE) Vehicles Rule for Model Years 2021-2026
Passenger Cars and Light Trucks,” 83 Federal Register 42986, August 24, 2018.
95
Ibid.
96 Ibid., p. 43232.
97 EPA and NHTSA, “The Safer, Affordable, Fuel-Efficient (SAFE) Vehicles Rule, Part One: One National Program,”
84 Federal Register 51310, September 27, 2019 (hereinafter 84 Federal Register 51310).
98 Ibid., p. 51313. NHTSA concluded that any state or local law or regulation regulating or prohibiting CO tailpipe
2
emissions from automobiles is “expressly and impliedly preempted by EPCA.” Ibid., p. 51356 (emphasis added). “Preemption may be either expressed or implied, and ‘is compelled whether Congress’ command is explicitly stated in the
statute’s language or implicitly contained in its structure and purpose.’” Gade v. Nat’l Solid Wastes Mgmt. Ass’n, 505
U.S. 88, 98 (1992) (quoting Jones v. Rath Packing Co., 430 U.S. 519, 525 (1977)). For further background on federal
preemption, see CRS Report R45825, Federal Preemption: A Legal Primer, by Bryan L. Adkins, Alexander H. Pepper,
and Jay B. Sykes (2023).
Congressional Research Service
16
California and the Clean Air Act (CAA) Waiver: Frequently Asked Questions
Congress can preempt state laws or regulations or allow states to act under certain
circumstances99 led NHTSA to several conclusions in the Part One rule.
EPCA’s preemption provisions state that when a federal fuel economy standard is in effect, a state
“may not adopt or enforce a law or regulation related to fuel economy standards or average fuel
economy standards for automobiles covered by an average fuel economy standard.”100 In 2019,
NHTSA explained that “as a practical matter, regulating fuel economy controls the amount of
tailpipe emissions of carbon dioxide, and regulating the tailpipe emissions of carbon dioxide
controls fuel economy.”101 Thus, NHTSA concluded in the 2019 Part One rule that any state or
local law that regulates or prohibits carbon dioxide (CO2) emissions from automobiles is related
to fuel economy standards and is therefore preempted under EPCA as invalid (i.e., void ab
initio).102
NHTSA also determined that EPCA preempted state and local zero-emission vehicle (ZEV)
mandates because they have a direct or substantial effect of regulating or prohibiting CO2 tailpipe
emissions from automobiles.103 For example, California’s ZEV program required that a certain
percentage of a manufacturer’s fleet of passenger cars, light-duty trucks, and medium-duty
vehicles sold in the state produce zero exhaust emissions of certain pollutants, including CO2.104
NHTSA reasoned that such ZEV mandates affect the average fuel economy achieved by the
manufacturer’s fleet.105 Thus, NHTSA concluded that EPCA preempts state ZEV mandates, such
as California’s ZEV program, because they are related to average fuel economy standards.106
Because NHTSA’s revised CAFE standards for MY2021-MY2026 went into effect in June
2020,107 EPCA preempted California GHG standards and ZEV mandates for those model years
under the interpretation articulated in the Part One rule.
NHTSA described certain state and local GHG requirements that EPCA would not preempt
because they have “no bearing on fuel economy.”108 For example, NHSTA noted that leaking
refrigerants from vehicle air conditioning units may emit GHGs when the unit is recharged or
when it is crushed at the end of the vehicle’s life.109 Because state or local laws specifically
regulating or prohibiting vehicular refrigerant leakage are not related to a vehicle’s fuel economy
or tailpipe CO2 emissions, NHTSA concluded that EPCA would not preempt such state or local
laws if they were narrowly drafted or severable from preempted tailpipe CO2 emissions
standards.110
99 See the section “What Is Federal Preemption of State Vehicle Emissions Standards?” in this report.
100 49 U.S.C. §32919(a) (emphasis added).
101 84 Federal Register 51310, p. 51313 (codified at 49 C.F.R. Parts 531, app. B; 533, app. B).
102 84 Federal Register 51310, p. 51324. Ab initio is defined as “[f]rom the beginning.” “Ab Initio,” in Black’s Law
Dictionary, 11th ed., Bryan A. Garner, ed. (Thomson Reuters, 2019).
103 84 Federal Register 51310, p. 51320.
104 Cal. Code Regs. tit. 13, §1962.2.
105 84 Federal Register 51310, p. 51320.
106 Ibid.
107 EPA and NHTSA, “The Safer Affordable Fuel-Efficient (SAFE) Vehicles Rule for Model Years 2021-2026
Passenger Cars and Light Trucks; Final Rule,” 85 Federal Register 24174, April 30, 2020.
108 84 Federal Register 51310, p. 51314.
109 Ibid.
110 Ibid.
Congressional Research Service
17
California and the Clean Air Act (CAA) Waiver: Frequently Asked Questions
NHTSA adopted regulatory text adding EPCA’s statutory preemption provisions and its
interpretation in new appendixes to Parts 551 and 553 of Title 49 of the Code of Federal
Regulations.111
EPA’s Interpretation of Section 209(b)
The 2019 Part One rule also addressed the CAA Section 209(b) preemption waiver that EPA had
granted California in 2013. This waiver covered California’s GHG and ZEV standards for
MY2021-MY2025 passenger cars and light- and medium-duty trucks.112 EPA concluded that the
2013 California preemption waiver was “invalid, null, and void” and withdrew it on two separate
grounds. First, EPA recognized NHTSA’s determination that EPCA preempts and voids ab initio
California CO2 tailpipe emissions standards and ZEV mandates.113 Second, EPA determined that
California did not need its GHG or ZEV standards for MY2021-MY2025 passenger cars, lightduty trucks, and medium-duty vehicles to meet “compelling and extraordinary conditions.”114
EPA’s decision to withdraw the waiver was based on an interpretation of CAA Section
209(b)(1)(B) that was different from its interpretation in the 2013 waiver decision. In 2013, EPA
reviewed whether California “needed” its motor vehicle program as a whole to reduce air
pollution, and not solely based on GHG standards addressed in the waiver request.115 Under that
approach, EPA concluded that it would not deny the waiver request because California had
“repeatedly” demonstrated the need for its motor vehicle program to address “compelling and
extraordinary” local and regional air pollution problems.116
In its 2019 interpretation, EPA concluded that the text of Section 209(b)(1)(B) requires the agency
to assess whether California needs the standards at issue in the waiver to address compelling and
extraordinary conditions, not whether California generally needs a separate state vehicle
emissions program to address air pollution from vehicles.117 EPA reasoned that Congress intended
“compelling and extraordinary conditions” to refer to state-specific pollution problems that have a
“particular nexus” to vehicle emissions and the health effects from such pollution.118 Based on
this interpretation of Section 209(b)(1)(B), EPA determined that global GHG emissions and their
effects are outside the scope of local or regional air pollution and do not present ‘‘compelling and
extraordinary conditions’’ specific to California.119 EPA explained that California does not “need”
its own vehicle GHG standards because the standards will not “meaningfully” address global air
pollution problems associated with GHG emissions.120 The withdrawal of the California waiver
became effective in November 2019.121
111 Ibid.
112 78 Federal Register 2112. For more information on the CAA’s preemption provisions, see the section “What Is the
Clean Air Act Waiver?” in this report.
113 84 Federal Register 51310, p. 51338.
114 Ibid., p. 51350.
115 78 Federal Register 2112.
116 Ibid., p. 2129.
117 84 Federal Register 51310, p. 51344.
118 Ibid., pp. 51340, 51350 (concluding that this interpretation of the “compelling and extraordinary” provision “is the
best, if not the only, reading of that provision.”). EPA’s interpretation appears similar, but not identical, to its reasoning
in a previous waiver denial in 2008. Ibid., pp. 51339-51340. EPA noted that its 2019 interpretation of CAA
§209(b)(1)(B) took a different approach from its 2008 waiver denial. Ibid.
119 Ibid., p. 51349.
120 Ibid., pp. 51340-51349.
121 Ibid., pp. 51310, 51350.
Congressional Research Service
18
California and the Clean Air Act (CAA) Waiver: Frequently Asked Questions
EPA’s Interpretation of Section 177
The waiver withdrawal also affected the states that had adopted the California motor vehicle
GHG emissions standards. CAA Section 177 allows states, under certain conditions, “to adopt
and enforce new motor vehicle emissions standards that are identical to the California standards
for which a waiver has been granted for [a given] model year.’’122 Section 177 requires that the
state adopting the standards have an approved CAA State Implementation Plan to meet or attain
national ambient air quality standards (NAAQS) for certain specified pollutants (ozone, carbon
monoxide, nitrogen dioxide, sulfur dioxide, lead, and particulate matter).123
At the time of the withdrawal, 14 additional states and the District of Columbia had adopted
California’s vehicle GHG standards, and 12 of those states had also adopted California’s ZEV
mandates.124 Because EPA withdrew the California waiver, these states and the District of
Columbia had no authority under CAA Section 177 to enforce these vehicle GHG standards in
their states, and no other states could adopt California’s GHG standards.
In the 2019 Part One rule, EPA also finalized a new interpretation narrowing the scope of CAA
Section 177. EPA concluded that Section 177 does not extend to California’s GHG standards
because this section applies only to California standards that address criteria pollutants that affect
regional or local air quality.125 EPA reasoned that Section 177 was intended to assist states in
reducing emissions of pollutants that are subject to the NAAQS, which tend to have more local
effects, and “not to address global air pollution” such as GHGs.126 Therefore, if EPA were to grant
California a waiver in the future for new motor vehicle standards for a global pollutant such as
GHGs, states would not be able to adopt those standards under EPA’s current interpretation of
Section 177’s applicability.
Actions Under the Biden Administration
In March 2022, EPA reissued the 2013 waiver for California’s Advanced Clean Cars (ACC) I
regulations (which covered California’s GHG and ZEV standards for MY2021-MY2025
passenger cars and light- and medium-duty trucks); at the same time, NHTSA repealed the SAFE
rule.127 In reissuing the waiver, EPA stated that it had limited ability to rescind previously granted
122 42 U.S.C. §7507.
123 Ibid.
124 States that adopted both California’s low emission vehicles (LEV) GHG standards and ZEV mandates at the time of
this rulemaking were Colorado, 5 Colo. Code Reg. §1001-24; Connecticut, Conn. Agencies Regs. §22a-174-36c;
Maine, 06-096-127 Me. Code R. §§1-12; Maryland, Md. Code Regs. 26.11.34.09; Massachusetts, 310 Mass. Code
Regs. 7.40; New Jersey, N.J. Admin. Code §7:27-29; New York, N.Y. Comp. Codes R. and Regs. tit. 6, §§218-4.1,
218-8.1-8.5; Oregon, Or. Admin. R. 340-257-0040, -0050, -0080; Rhode Island, 250-120 R.I. Code R. Part 37;
Vermont, 12-031-001 Vt. Code R. §5-1106(6); Virginia, 2021 Va. Leg. Serv. 1st Sp. sess. ch. 263 (H.B. 1965) (West);
and Washington, Wash. Rev. Code §70A.30.010, Wash. Admin. Code 173-423-050. States that adopted LEV GHG
standards only are Delaware, 7-1000-1140 Del. Admin. Code §5; Pennsylvania, 25 Pa. Code §126.411; and the District
of Columbia, D.C. Code §50-731. Minnesota, Nevada, and New Mexico are considering adopting California’s vehicle
GHG standards. See “Proposed Permanent Rules Relating to Clean Cars; Notice of Intent to Adopt Rules with a
Hearing,” 45 Minn. Reg. 663, December 21, 2020; Nevada Division of Environmental Protection, “Clean Cars
Nevada,” https://ndep.nv.gov/air/clean-cars-nevada, accessed January 27, 2021; New Mexico Governor Michelle Lujan
Grisham, “Executive Order on Addressing Climate Change and Energy Waste Prevention,” Exec. Order 2019-003,
January 29, 2020, https://www.governor.state.nm.us/wp-content/uploads/2019/01/EO_2019-003.pdf.
125 84 Federal Register 51310, p. 51350.
126 Ibid., p. 51351.
127 EPA, “California State Motor Vehicle Pollution Control Standards; Advanced Clean Car Program; Reconsideration
of a Previous Withdrawal of a Waiver of Preemption; Notice of Decision,” 87 Federal Register 14332, March 14, 2022
(continued...)
Congressional Research Service
19
California and the Clean Air Act (CAA) Waiver: Frequently Asked Questions
waivers and that the SAFE rule that withdrew the ACC I waiver exceeded the agency’s
authority.128 EPA also concluded that its rescission of the ACC I waiver was based on a flawed
interpretation of Section 209(b) and that it had improperly considered preemption under EPCA as
a basis for rescinding the waiver.129 EPA’s reissuance of the waiver was challenged in Ohio v.
EPA.130 As discussed in more detail below, the U.S. Court of Appeals for the D.C. Circuit (D.C.
Circuit) sustained EPA’s decision.131 NHTSA, for its part, concluded that in issuing the SAFE rule
it had exceeded its authority to issue a regulation interpreting the scope of preemption under
EPCA.132
EPA’s and NHTSA’s Reinterpretation of EPCA Preemption
In EPA’s 2022 reissuance of the 2013 waiver, EPA determined that it was improper for EPA in the
SAFE rule to consider EPCA preemption when determining whether to rescind the waiver for
ACC I.133 Section 209(b) lists the statutory factors by which EPA must evaluate whether to grant a
waiver.134 EPCA preemption is not among these factors.135 According to EPA, it was improper for
EPA to consider a factor that Congress did not intend it to consider.136
Moreover, NHTSA, the agency entrusted to administer EPCA, had formally withdrawn its
conclusions that state or local regulations of tailpipe CO2 emissions are “related to” fuel economy
standards and therefore preempted under EPCA.137 Accordingly, EPA explained, even if it could
consider EPCA preemption in its evaluation of a waiver, the predicate (i.e., NHTSA’s 2019
preemption determination) for EPA’s prior decision to withdraw the ACC I waiver no longer
existed.138
NHTSA withdrew its conclusions regarding preemption of state and local GHG emissions
regulations because it too found that the earlier conclusions rested on flawed interpretations of
EPCA.139 In its 2021 withdrawal, NHTSA determined that Section 32919, the preemption
provision of EPCA, does not confer on NHTSA rulemaking authority to issue regulations
interpreting the scope of preemption under EPCA.140 NHTSA also determined that its preemption
regulations ignored “substantially important federalism interests” and “failed to account for
(hereinafter 87 Federal Register 14332); NHTSA, “Corporate Average Fuel Economy (CAFE) Preemption,” 86
Federal Register 74236, December 29, 2021 (hereinafter 86 Federal Register 74236).
128 87 Federal Register 14332, p. 14344.
129 Ibid., pp. 14352, 14368.
130 98 F.4th 288 (D.C. Cir. 2024).
131 Ibid. The Supreme Court agreed to review the D.C. Circuit’s decision but only as to whether the petitioners had
standing to challenge the waiver on statutory grounds. See Order, Diamond Alternative Energy, LLC v. EPA, No. 24-7
(U.S. December 13, 2025).
132 86 Federal Register 74236, p. 74238.
133 Ibid., p. 14368. Two district court cases have evaluated the interaction between EPCA’s preemption provision and
Section 209(b). Both found that EPCA’s preemption provision does not preempt California from adopting GHG
standards, nor does it preclude EPA from issuing a waiver for such standards. Both cases are discussed in more detail
below. See “Conflicts with the Energy Policy and Conservation Act (EPCA).”
134 42 U.S.C. §7543(b)(1).
135 Ibid.
136 87 Federal Register 14332, p. 14369.
137 Ibid., p. 14371; 86 Federal Register 74236, p. 74238.
138 87 Federal Register 14332, p. 14369.
139 86 Federal Register 74236, p. 74238.
140 Ibid.
Congressional Research Service
20
California and the Clean Air Act (CAA) Waiver: Frequently Asked Questions
legally relevant factors, such as reliance interests of states and local jurisdictions in longstanding
programs.”141
EPA’s Reinterpretation of Section 209(b)(1)(B): “Compelling and Extraordinary
Conditions”
Pursuant to Section 209(b)(1)(B), EPA must grant a waiver unless California “does not need such
State standards to meet compelling and extraordinary conditions.”142 In the SAFE rule, EPA
interpreted this provision as requiring EPA to evaluate whether California needs each standard for
a particular pollutant (e.g., NOX) to meet compelling and extraordinary circumstances.143
In the 2022 waiver, EPA returned to the interpretation it put forward in its original 2013 waiver.144
It reinterpreted “such State standards” in light of Section 209(b)(1), which requires California to
determine that its standards are “in the aggregate at least as protective” as the federal standards.145
According to EPA and contrary to the SAFE rule, California’s need for a waiver must be
evaluated based on the “aggregate” of all of California’s regulations subject to waivers—not
based on whether the standard for a specific pollutant is more stringent than the federal
standards.146 This interpretation, EPA reasons, gives meaning to the term “aggregate” in Section
209(b)(1) and ensures that both EPA and California “review the same standards that California
considers in making its protectiveness determination.”147
EPA similarly found flaws in its own determination in the SAFE Rule that California did not
“need” the ACC I regulations to meet “compelling and extraordinary conditions.”148 EPA noted
that ACC I serves to reduce both GHG emissions and emissions of criteria pollutants.149 A
consequence of reducing GHG emissions is a reduction in criteria pollutants.150 Moreover, by
increasing the number of cars sold that emit no emissions whatsoever, ACC I will further reduce
criteria pollutant emissions.151 According to EPA, California air suffers from high levels of some
criteria pollutants and the ACC I regulations will help alleviate that problem.152
EPA went on, however, to explain that California “needs” the ACC I standards to address the
impacts of climate change on California.153 California, EPA determined, is particularly affected by
global climate change, “including increasing risk from record-setting fires, heat waves, storm
surges, sea-level rise, water supply shortages and extreme heat.”154 Locally elevated CO2 can also
have local impacts on, for instance, ocean acidification along California’s coast.155 “Thus, like
criteria pollution, emissions of [greenhouse gases] can lead to locally elevated concentrations
141 Ibid., pp. 74328-74329.
142 42 U.S.C. §7543(b)(1)(B).
143 84 Federal Register 51310, p. 51344.
144 87 Federal Register 14332, p. 14358.
145 Ibid.
146 Ibid.
147 Ibid.
148 Ibid., p. 14363.
149 Ibid.
150 Ibid., p. 14364.
151 Ibid.
152 Ibid.
153 Ibid., p. 14365.
154 Ibid.
155 Ibid., p. 14366.
Congressional Research Service
21
California and the Clean Air Act (CAA) Waiver: Frequently Asked Questions
with local impacts, in addition to the longer-term global impacts resulting from global increases
in [greenhouse gas] concentrations.”156
Finally, EPA determined that Section 209(b)(1)(B) does not require California’s ACC I
regulations to “independently solve” global climate change.157 Although ACC I will not by itself
reduce GHG emissions enough to prevent impacts from climate change from affecting California,
“California’s policy judgment that an incremental, directional improvement will occur and is
worth pursuing is entitled ... to great deference.”158
EPA’s Reinterpretation of Section 177
In the SAFE rule, EPA interpreted Section 177, which permits states to adopt California
emissions standards that have received a waiver, as not permitting states to adopt California’s
GHG standards.159 In its 2022 waiver reissuance, EPA determined that this interpretation was
flawed and withdrew it.160 EPA first noted that Section 177 provides no role for EPA
whatsoever:161 Section 177 simply provides states authority to adopt California standards that
have been granted a waiver by EPA.162 Accordingly, EPA’s prior interpretation was
“nonregulatory and nonbinding.”163 EPA further determined that, because it plays no role in
states’ ability to adopt California standards under Section 177, it was “inappropriate” for it “to
offer an interpretive view” of Section 177.164
Actions Under the Second Trump Administration
In January 2025, the Trump Administration issued Executive Order 14154, which stated that “it is
the policy of the United States” to take actions including “to eliminate” the “electric vehicle (EV)
mandate” by, among other actions, “terminating, where appropriate, state emissions waivers that
function to limit sales of gasoline-powered automobiles.”165
In February 2025, EPA submitted three waivers granted during the Biden Administration to
Congress for review under the CRA (see “Can Clean Air Act Waivers Be Reviewed Under the
Congressional Review Act?”).166
156 Ibid.
157 Ibid.
158 Ibid.
159 84 Federal Register 51310, p. 51350.
160 87 Federal Register 14332, p. 14374.
161 Ibid., p. 14375.
162 Ibid.; 42 U.S.C. §7507.
163
87 Federal Register 14332, p. 14375.
164 Ibid.
165 90 Federal Register 8353.
166 EPA, “California State Motor Vehicle and Engine Pollution Control Standards; Heavy-Duty Vehicle and Engine
Emission Warranty and Maintenance Provisions; Advanced Clean Trucks; Zero Emission Airport Shuttle; ZeroEmission Power Train Certification; Waiver of Preemption; Notice of Decision” 88 Federal Register 20688, April 6,
2023 (Advanced Clean Trucks); EPA, “California State Motor Vehicle and Engine and Nonroad Engine Pollution
Control Standards; The ‘‘Omnibus’’ Low NOX Regulation; Waiver of Preemption; Notice of Decision,” 90 Federal
Register 643, January 6, 2025 (Heavy-Duty Omnibus); EPA, “California State Motor Vehicle and Engine Pollution
Control Standards; Advanced Clean Cars II; Waiver of Preemption; Notice of Decision” Advanced Clean Cars II
Waiver Notice,” 90 Federal Register 642, January 6, 2025 (Advanced Clean Cars II).
Congressional Research Service
22
California and the Clean Air Act (CAA) Waiver: Frequently Asked Questions
In March 2025, as part of a deregulatory effort across numerous programs, EPA announced that it
would reconsider the federal GHG motor vehicle emissions standards.167
What Actions Has Congress Taken Regarding the
Waiver Authority?
As of April 2025, six bills have been introduced in recent Congresses that seek to modify or
revoke California’s federal preemption waiver authority under CAA Section 209(b).168
119th Congress
As of April 2025, three bills have been introduced in the 119th Congress that seek to modify or
revoke California’s federal preemption waiver authority under CAA Section 209(b).
H.R. 346: Preserving Choice in Vehicle Purchases Act
H.R. 346 would amend Section 209(b) of the CAA to prohibit EPA from issuing waivers to states
that directly or indirectly limit the sale or use of new motor vehicles with internal combustion
engines. In addition, the bill would require EPA to revoke waivers granted between January 2022
and the date of enactment of the bill. H.R. 346 was introduced in the House on January 13, 2025,
and referred to the House Committee on Energy and Commerce.169
S. 996: Preserving Choice in Vehicle Purchases Act of 2025
S. 996 is the Senate companion bill to H.R. 346. S. 996 would amend Section 209(b) of the CAA
to prohibit EPA from issuing waivers to states that directly or indirectly limit the sale or use of
new motor vehicles with internal combustion engines. In addition, the bill would require EPA to
revoke waivers granted between January 2022 and the date of enactment of the bill. S. 996 was
introduced in the Senate on March 12, 2025 and referred to the Committee on Environment and
Public Works.
H.R. 2218: Stop California from Advancing Regulatory Burden Act of 2025
(Stop CARB Act of 2025)
H.R. 2218 would amend Section 209(b) of the CAA by repealing the waiver authority under
Section 209(b) allowing California to adopt or attempt to enforce emission control standards on
new motor vehicles. In addition, the bill would prohibit state-level emissions standards for
nonroad engines and vehicles. The bill would nullify existing waivers and deny any pending
applications. H.R. 2218 was introduced to the House on March 18, 2025, and referred to the
Committee on Energy and Commerce.170
167 EPA, “EPA Launches Biggest Deregulatory Action in U.S. History,” press release, 2025,
https://www.epa.gov/newsreleases/epa-launches-biggest-deregulatory-action-us-history.
168 CRS searched for bills introduced during the 116th-119th Congresses on Congress.gov using the keywords motor
vehicle, Clean Air Act, Section 209(b), and waiver. Search results are current as of April 6, 2025.
169 All actions, H.R. 346 – Preserving Choice in Vehicles Act, https://www.congress.gov/bill/119th-congress/housebill/346/all-actions.
170 All actions, H.R. 2218 – Stop CARB Act, https://www.congress.gov/bill/119th-congress/house-bill/2218/all-actions.
Congressional Research Service
23
California and the Clean Air Act (CAA) Waiver: Frequently Asked Questions
118th Congress
Two bills were introduced in the 118th Congress that sought to modify or revoke California’s
federal preemption waiver authority under CAA Section 209(b).171
H.R. 1435: Preserving Choice in Vehicle Purchases Act
H.R. 1435 would have amended Section 209(b) of the CAA to prohibit EPA from issuing waivers
to states that directly or indirectly limit the sale or use of new motor vehicles with internal
combustion engines. In addition, the bill would have required EPA to revoke waivers granted
between January 2022 and the date of enactment of the bill. H.R. 1435 was introduced in the
House on March 8, 2023, and referred to the House Subcommittee on Environment,
Manufacturing, and Critical Materials and the House Committee on Energy and Commerce.172 On
September 14, 2023, the bill passed the House 222-190 by Yeas and Nays vote.173 The bill was
received in the Senate and was referred to the Senate Committee on Environment and Public
Works on September 18, 2023. The Senate took no subsequent action on the bill.174
In June 2023, the House Committee on Energy and Commerce, Subcommittee on Environment,
Manufacturing, and Critical Materials, held a hearing titled Driving Affordability: Preserving
People’s Freedom to Buy Affordable Vehicles and Fuel.175 The hearing discussed four pieces of
legislation, including H.R. 1435. Statements from the Subcommittee Chair, Ranking Member,
and witnesses reflected a range of views regarding H.R. 1435. A selected and abridged sample of
these statements includes the following:
•
•
•
Chair Representative Bill Johnson: “The intent of the Clean Air Act is clear.
Congress never directed California to dictate America’s vehicle emissions, and
also did not authorize the EPA to force vehicles that the agency does not like off
the road.”176
Ranking Member Representative Paul Tonko: “Given its history and
extraordinary air quality challenges, California has the ability to request the
preemption waiver for its vehicle emission standards, provided that they are at
least as stringent as federal standards, necessary to meet compelling and
extraordinary conditions.”177
Joseph Goffman, Principal Deputy Administrator for the Office of Air and
Radiation at EPA: “Congress granted California the authority to regulate
emissions from vehicles over 50 years ago and continually re-enacted that
authority through periodic reauthorizations of the Clean Air Act. Congress sought
171 CRS searched for bills introduced during the 116 th-119th Congresses on Congress.gov using the keywords motor
vehicle, Clean Air Act, Section 209(b), and waiver. Search results are current as of April 6, 2025.
172 All actions, H.R. 1435 – Preserving Choice in Vehicles Act, https://www.congress.gov/bill/118th-congress/housebill/1435/all-actions.
173 House of Representatives Roll Call Vote number 391, 118th Cong., 1st sess., September 14, 2023,
https://clerk.house.gov/Votes/2023391.
174 All actions, H.R. 1435 – Preserving Choice in Vehicles Act, https://www.congress.gov/bill/118th-congress/housebill/1435/all-actions.
175 U.S. Congress, House Energy and Commerce Committee, Subcommittee on Environment, Manufacturing, and
Critical Materials, Driving Affordability, Preserving People’s Freedom to Buy Affordable Vehicles and Fuel, hearings,
118th Cong., 1st sess., June 22, 2023 (hereinafter Driving Affordability hearing), https://congressional.proquest.com/
congressional/docview/t39.d40.tr06220123.o15?accountid=12084.
176 Ibid.
177 Ibid.
Congressional Research Service
24
California and the Clean Air Act (CAA) Waiver: Frequently Asked Questions
•
•
•
to give the state the power to address its unique and ongoing air quality
challenges and to give other states the option to adopt the innovative clean car
and truck technologies California pioneered.”178
Neil Caskey, CEO, National Corn Growers Association: “We support uniform
vehicle standards for both fuel economy and GHG emissions, relying on a full
lifecycle analysis to ensure a level playing field for all types of fuels and
vehicles.”179
Chet Thompson, President and CEO, American Fuel and Petrochemical
Manufacturers: “The Choice in Automobile Retail Sales Act of 2023 and
Preserving Choice in Vehicle Purchases Act do not prevent EPA from setting
tailpipe standards, nor do they prevent California from seeking waivers to
address compelling and extraordinary conditions unique to Californians. The bills
simply reaffirm the fact that EPA and California do not have the authority to ban
vehicle powertrain technologies and limit mobility options for consumers.”180
Genevieve Cullen, President, Electric Drive Transportation Association: “At this
inflection point for the market, this disruption and uncertainty would work
against U.S. market leadership and consumers’ access to EV choices. Vehicle
manufacturers and the complex supply chains that support them, and the EV
ecosystem, have made substantial investments in reliance on the current
regulatory regimes.”181
The committee report accompanying H.R. 1435 (H.Rept. 118-169) indicated that the bill was
proposed in response to CARB’s August 2022 decision to approve a regulation that would limit
the sale of new internal combustion engine vehicles in California and promote the sale of zeroemission vehicles.182 The report emphasized the cost and functionality of electric vehicles and
current consumer preferences as justification to amend CAA Section 209(b) and to thereby
prevent CARB from promulgating its proposed regulation. The committee found that H.R. 1435
would not result in new or increased budget authority, entitlement authority, or tax expenditures
or revenues. There was no Congressional Budget Office (CBO) estimate for the bill at the time
the report was filed.
The minority views opposed H.R. 1435 on the grounds that it would upend the electric vehicle
supply chain and create uncertainty for the automotive industry.183 The minority also recognized
California as a leader in setting air pollution standards.184
178 Written testimony of Joseph Goffman, Driving Affordability hearing, https://docs.house.gov/meetings/IF/IF18/
20230622/116147/HHRG-118-IF18-Wstate-GoffmanJ-20230622.pdf.
179 Written testimony of Neil Caskey, Driving Affordability hearing, https://docs.house.gov/meetings/IF/IF18/
20230622/116147/HHRG-118-IF18-Wstate-CaskeyN-20230622.pdf.
180 Written testimony of Chet Thompson, Driving Affordability hearing, https://docs.house.gov/meetings/IF/IF18/
20230622/116147/HHRG-118-IF18-Wstate-ThompsonC-20230622.pdf.
181 Written testimony of Genevieve Cullen, Driving Affordability hearing, https://docs.house.gov/meetings/IF/IF18/
20230622/116147/HHRG-118-IF18-Wstate-CullenG-20230622.pdf.
182 U.S. Congress, House Committee on Energy and Commerce, Preserving Choice in Vehicle Purchases Act, report to
accompany H.R. 1435, 118th Cong., 1st sess., H.Rept. 118-169, p. 3.
183 Ibid., p. 15.
184 Ibid.
Congressional Research Service
25
California and the Clean Air Act (CAA) Waiver: Frequently Asked Questions
H.R. 4468: Choice in Automobile Retail Sales Act of 2023
H.R. 4468 would have amended Section 209(b) of the CAA to prohibit EPA from issuing waivers
to states that mandate the use of the technology or result in the limited availability of new motor
vehicles based on the type of engine. In addition, this bill would have required EPA “to
promulgate revisions to regulations as may be necessary to conform such regulations to section
202(a)(2)(B) of the Clean Air Act, as added by subsection (a).”
H.R. 4468 was introduced in the House on July 6, 2023, and passed the House on December 6,
2023. It was received in the Senate on December 7, 2023, and referred to the Committee on
Environment and Public Works.185
S. 2090: Preserving Choice in Vehicle Purchases Act of 2023
S. 2090 was the Senate companion bill to H.R. 1435. S. 2090 would have amended Section
209(b) of the CAA to prohibit EPA from issuing waivers to states that directly or indirectly limit
the sale or use of new motor vehicles with internal combustion engines. In addition, the bill
would have required EPA to revoke waivers granted between January 2022 and the date of
enactment of the bill. S. 2090 was introduced in the Senate on June 21, 2023, and referred to the
Senate Committee on Environment and Public Works.186 No further action was taken on the bill.
117th Congress
One bill was introduced in the 117th Congress that sought to revoke California’s federal
preemption waiver authority under CAA Section 209(b).187
H.R. 8773: Revoking Engine and Vehicle Requirements Act of 2022
H.R. 8773 would have amended the CAA by repealing the waiver authority under Section 209(b)
allowing California to adopt or attempt to enforce emission control standards on new motor
vehicles. H.R. 8773 was introduced in the House on September 6, 2022, and then referred to the
House Committee on Energy and Commerce and the Subcommittee on Environment and Climate
Change.188 No further action was taken on the bill.
Can Clean Air Act Waivers Be Reviewed Under the
Congressional Review Act?
Questions have arisen as to whether California’s CAA federal preemption waivers are covered by
the Congressional Review Act’s (CRA’s) definition of rule and therefore eligible to be overturned
under the CRA. The Government Accountability Office (GAO), to which the Senate has generally
deferred on questions regarding the CRA’s eligibility, has stated that the waivers are not
185 All actions, H.R. 4468 – Choice in Automobile Retail Sales Act of 2023, https://www.congress.gov/bill/118th-
congress/house-bill/4468/all-actions.
186 All actions, S. 2090 – Preserving Choice in Vehicle Purchases Act of 2023, https://www.congress.gov/bill/118thcongress/senate-bill/2090/all-actions.
187 CRS searched for bills introduced during the 116 th-119th Congresses on Congress.gov using the keywords motor
vehicle, Clean Air Act, Section 209(b), and waiver. Search results are current as of April 6, 2025.
188 All actions, H.R. 8773 – Revoking Engine and Vehicle Requirements Act of 2022, https://www.congress.gov/bill/
117th-congress/house-bill/8773/all-actions.
Congressional Research Service
26
California and the Clean Air Act (CAA) Waiver: Frequently Asked Questions
covered.189 EPA’s position on whether they are covered has changed over time, with the current
Administration arguing that they are covered.190
The CRA (5 U.S.C. §§801-808) provides a mechanism for Congress to review federal agency
actions that meet the CRA’s definition of rule.191 Enacted in 1996, the CRA requires agencies to
report the issuance of rules to Congress and provides Congress with special fast-track procedures
under which to consider legislation that overturns a rule.192 Pursuant to the CRA, Congress can
nullify a rule by a joint resolution of disapproval that passes both houses of Congress and is
signed by the President or through a two-thirds majority vote in each house if the President vetoes
the resolution.193
For an agency action to be eligible for review under the CRA, it must qualify as a rule as defined
by the CRA.194 The CRA adopts the definition of rule contained in the Administrative Procedure
Act (APA), though it creates three exceptions to that definition.195 Importantly, the CRA does not
apply to orders or rules of particular applicability issued by agencies.
The APA defines two primary categories of agency actions—rules and orders. The APA defines a
rule as “the whole or a part of an agency statement of general or particular applicability and
future effect designed to implement, interpret, or prescribe law or policy.”196 The APA’s definition
of rule, however, does not include agency actions known as orders.197 Orders are the product of
agency adjudications.198 The APA defines order as “the whole or part of a final disposition ... of
an agency in a matter other than a rule making but including licensing.”199
Taken together, in the words of one federal court of appeals, the definitions provide that “[a]n
adjudication ... is virtually any agency action that is not rulemaking.”200 As a general matter,
“adjudications resolve disputes among specific individuals in specific cases, whereas rulemaking
189 See U.S. Government Accountability Office, “Environmental Protection Agency—Applicability of the
Congressional Review Act to Notice of Decision on Clean Air Act Waiver of Preemption,” B-334309, November 30,
2023; U.S. Government Accountability Office, “Observations Regarding the Environmental Protection Agency’s
Submission of Notices of Decision on Clean Air Act Preemption Waivers as Rules Under the Congressional Review
Act,” B- 337179, March 6, 2025.
190 Compare 88 Federal Register at 20725; 90 Federal Register at 645; 90 Federal Register at 643, with EPA, “Trump
EPA to Transmit California Waivers to Congress in Accordance with Statutory Reporting Requirements,” February 14,
2025, https://www.epa.gov/newsreleases/trump-epa-transmit-california-waivers-congress-accordance-statutoryreporting.
191 See 5 U.S.C. §§801, 804. For more information about the CRA, see CRS Report R45248, The Congressional
Review Act: Determining Which “Rules” Must Be Submitted to Congress, by Valerie C. Brannon and Maeve P. Carey
(2024) (hereinafter The Congressional Review Act); CRS Report R43992, The Congressional Review Act (CRA):
Frequently Asked Questions, by Maeve P. Carey and Christopher M. Davis (2021).
192 5 U.S.C. §§801-808. For further explanation regarding these fast-track procedures, see The Congressional Review
Act, supra footnote 191
193
5 U.S.C. §801.
194 Ibid.; 5 U.S.C. §804(3) (defining “rule”).
195 5 U.S.C. §804(3). The APA’s definition of rule is contained in Section 551(4). 5 U.S.C. §551(4). Not all agency
actions defined as rules, however, are required to go through notice and comment rulemaking as outlined in Section
553. See 5 U.S.C. §553.
196 5 U.S.C. §551(4).
197 Ibid.
198 Ibid. §551(7).
199 Ibid. §551(6).
200 Yesler Terrace Cmty. Council v. Cisneros, 37 F.3d 442, 448 (9th Cir. 1994).
Congressional Research Service
27
California and the Clean Air Act (CAA) Waiver: Frequently Asked Questions
affects the rights of broad classes of unspecified individuals.”201 Further, adjudications impose
“immediate effect[s]” on parties in a proceeding, while rulemakings are “prospective” in nature
and have “a definitive effect on individuals only after the rule subsequently is applied.”202
The CRA also excludes rules of particular applicability.203 This category of agency action has
some characteristics of a rule and some characteristics of an order. The term refers to “legislativetype promulgations” that are “directed to” specifically named parties.204 The CRA’s text gives
specific examples of rules of particular applicability, including “a rule that approves or prescribes
for the future rates, wages, prices, services, or allowances therefor.”205
Because the CRA’s special procedures are not available until rules are submitted to Congress, if
an agency does not submit a rule, this could potentially frustrate the purpose of the CRA.206
Under a process that has developed since the CRA’s enactment, Members of Congress who think
a particular agency action should have been submitted have asked GAO for a formal opinion on
whether the action satisfies the CRA definition of rule.207 If GAO determines the action is a rule,
the Senate has chosen to allow GAO’s opinion to trigger the CRA process, despite the agency not
having submitted the action.208
In March 2022, EPA issued a notice that reinstated the 2013 waiver for California’s ACC I
regulations that had previously been withdrawn in 2019.209 EPA did not submit the notice to
Congress pursuant to the CRA, stating that its action was not a covered rule.210 A Member of
Congress asked GAO to review the notice to determine whether the notice was a rule pursuant to
the CRA.211 On November 30, 2023, GAO issued an opinion determining that EPA’s
reinstatement of a waiver for California regulations setting emissions standards for GHG
emissions from cars and trucks was an “adjudicatory order” not subject to the CRA.212 GAO
explained that the waiver notice was a “final disposition granting California a form of permission
which meets the definition of order.”213 GAO added that the waiver notice was particular to
California, based on consideration of particular facts, and had immediate effect in California.214 In
the alternative, GAO concluded that the waiver decision qualified as a rule of particular
applicability because it “concerns a specific entity—California—and addresses a statutory waiver
specific to California’s Advanced Clean Car Program.”215
201 Ibid.; United States v. Fla. E. Coast Ry. Co., 410 U.S. 224, 245-246 (1973); see also Michael Asimow and Ronald
M. Levin, State and Federal Administrative Law, 3rd ed. (West Academic, 2009), p. 62.
202 Yesler Terrace Cmty., 37 F.3d at 448.
203 5 U.S.C. §804(3)(A).
204 U.S. Steel Corp. v. EPA, 605 F.2d 283, 285 n.3 (7th Circ. 1979) (discussing APA's legislative history).
205 5 U.S.C. §804(3)(A).
206 The Congressional Review Act, supra footnote 191.
207 Ibid.
208 Ibid.
209 U.S. Government Accountability Office, “Environmental Protection Agency—Applicability of the Congressional
Review Act to Notice of Decision on Clean Air Act Waiver of Preemption,” B-334309, November 30, 2023.
210 Ibid., p. 1; EPA, “California State Motor Vehicle Pollution Control Standards; Advanced Clean Car Program;
Reconsideration of a Previous Withdrawal of a Waiver of Preemption; Notice of Decision,” 87 Federal Register 14332,
14379 (March. 14, 2022).
211 Ibid.
212 Ibid., p. 3.
213 Ibid., p. 5.
214 Ibid., pp. 5-6.
215 Ibid., p. 6.
Congressional Research Service
28
California and the Clean Air Act (CAA) Waiver: Frequently Asked Questions
In late February 2025, the Trump Administration submitted three waivers (ACC II, Heavy-Duty
Omnibus, and Advanced Clean Trucks) granted during the Biden Administration to Congress for
review under the CRA.216 As with prior California waivers, EPA did not submit the waivers to
Congress at the time they were granted, because at that time EPA believed the waivers were not
subject to the CRA.217 In response to a request from three Senators, GAO issued “Observations”
restating its position in its 2023 opinion that waivers granted to California under Section 209 of
the Clean Air Act are orders, not rules.218 Notwithstanding GAO’s nonbinding opinion, some
Members introduced joint resolutions of disapproval in both chambers of Congress for all three
waivers.219 On April 4, 2025, the Senate Parliamentarian reportedly determined that the CRA does
not apply to the waivers submitted by EPA.220 On April 30 and May 1, 2025, the House passed all
three joint resolutions. The Senate has yet to take action on the resolutions.
What Actions Have Been Taken in the Federal
Courts Regarding the Waiver?
The California waiver has not been the subject of much litigation since its inclusion in the Air
Quality Act of 1967. Only since 2019 have EPA’s decisions to grant or rescind waivers been
subject to sustained legal challenge.221 Many of these more recent challenges arose in relation to
California’s regulation of GHG emissions.222 A number of these legal challenges went unresolved
216 EPA, “California State Motor Vehicle and Engine Pollution Control Standards; Heavy-Duty Vehicle and Engine
Emission Warranty and Maintenance Provisions; Advanced Clean Trucks; Zero Emission Airport Shuttle; ZeroEmission Power Train Certification; Waiver of Preemption; Notice of Decision,” 88 Federal Register 20688, April 6,
2023 (Advanced Clean Trucks); EPA, “California State Motor Vehicle and Engine and Nonroad Engine Pollution
Control Standards; The ‘‘Omnibus’’ Low NOX Regulation; Waiver of Preemption; Notice of Decision,” 90 Federal
Register 643, January 6, 2025 (Heavy-Duty Omnibus); EPA, “California State Motor Vehicle and Engine Pollution
Control Standards; Advanced Clean Cars II; Waiver of Preemption; Notice of Decision” Advanced Clean Cars II
Waiver Notice,” 90 Federal Register 642, January 6, 2025 (Advanced Clean Cars II).
217 See 88 Federal Register at 20725; 90 Federal Register at 645; 90 Federal Register at 643. CRS was unable to
identify an instance prior to 2025 when EPA submitted a preemption waiver for California’s vehicle emissions
regulations under Section 209 of the Clean Air Act.
218 U.S. Government Accountability Office, “Observations Regarding the Environmental Protection Agency’s
Submission of Notices of Decision on Clean Air Act Preemption Waivers as Rules Under the Congressional Review
Act,” B- 337179, March 6, 2025. Commentators disagree whether California waivers are subject to the CRA. Compare
Michael Buschbacher & Jimmy Conde, Congress Has the Authority to Review EPA “Waivers” of Clean Air Act
Preemption, NOTICE & COMMENT, YALE J. ON REGUL. BLOG (Mar. 5, 2025) https://www.yalejreg.com/nc/congress-hasthe-authority-to-review-epa-waivers-of-clean-air-act-preemption-by-michael-buschbacher-jimmy-conde/; and Michael
Buschbacher & Jimmy Conde, More Thoughts on Why the Congressional Review Act Applies to EPA “Waivers” of
Clean Air Act Preemption, NOTICE & COMMENT, YALE J. ON REGUL. BLOG (March 31, 2025)
https://www.yalejreg.com/nc/more-thoughts-on-why-the-congressional-review-act-applies-to-epa-waivers-of-clean-airact-preemption-by-michael-buschbacher-jimmy-conde/; with Daniel Farber, The Congressional Review Act and the
California Emissions Waiver: A Deeper Dive, NOTICE & COMMENT, YALE J. ON REGUL. BLOG (March 11, 2025)
https://www.yalejreg.com/nc/the-congressional-review-act-and-the-california-emissions-waiver-a-deeper-dive-bydaniel-farber/.
219 H.J. Res 87, 88, 89; S.J. Res. 45, 46, 47.
220 Rachel Frazin, Senate parliamentarian says lawmakers can’t overturn California car rules — but Republicans may
try anyway, THE HILL (April 4, 2025) https://thehill.com/policy/energy-environment/5233436-senate-parliamentariansays-lawmakers-cant-overturn-california-car-rules-but-republicans-may-try-anyway/.
221 See, for example, Union of Concerned Scientists v. NHTSA, No. 19-1230 (D.C. Cir.) (challenging, among other
things, EPA’s withdrawal of California’s waiver for its Advanced Clean Cars [ACC] I program); Ohio v. EPA, 98 F.4th
288 (D.C. Cir. 2024) (per curiam) (challenging EPA’s reinstatement of the waiver for California’s ACC I program).
222 Union of Concerned Scientists v. NHTSA, No. 19-1230 (D.C. Cir.) (challenging, among other things, EPA’s
(continued...)
Congressional Research Service
29
California and the Clean Air Act (CAA) Waiver: Frequently Asked Questions
by the courts because the Biden Administration reversed course on some actions carried out by
the Trump Administration before the courts could render decisions on the merits.223 Although the
change in administration left some disputes unresolved, those disputes are likely to be the subject
of future challenges in the federal courts. The courts have, however, rendered a handful of
decisions addressing the constitutionality of the California waiver and its relationship with EPCA.
The Constitutionality of Section 209(b): The Equal Sovereignty
Doctrine
In the 2024 case Ohio v. EPA, the U.S. Court of Appeals for the D.C. Circuit (D.C. Circuit) held
that Section 209(b) did not violate the equal sovereignty doctrine of the U.S. Constitution.224 In
2013, EPA granted a waiver to California to regulate GHG emissions from cars and light trucks in
MY2017-MY2025.225 The regulation was known as the ACC I rule. In 2019, EPA rescinded the
waiver for ACC I.226 Then, in 2022, EPA reinstated the waiver.227 A group of states and industry
associations brought suit against EPA for reinstating the waiver for the ACC I rule, arguing,
among other things, that Section 209(b) violates the equal sovereignty doctrine of the
Constitution.228
The equal sovereignty doctrine is a limitation on Congress’s legislative power.229 Where it
applies, it limits Congress’s authority to enact legislation that treats different states differently
without sufficient justification.230 The Supreme Court has invoked the doctrine on just two
occasions, both in the voting rights context.231
In Shelby County v. Holder, the Supreme Court struck down Section 5 of the Voting Rights Act
(VRA) as unconstitutional.232 To remedy the racial discrimination in voting that was endemic
during the Jim Crow era, the VRA required jurisdictions with a history of racial discrimination
against voters to obtain “preclearance” from the Department of Justice or a federal court before
changing their voting procedures.233 The Court held, “a departure from the fundamental principle
of equal sovereignty requires a showing that a statute’s disparate geographic coverage is
sufficiently related to the problem that it targets.”234 The Court found increases in African
withdrawal of California’s waiver for its ACC I program); Ohio v. EPA, 98 F.4th 288 (D.C. Cir. 2024) (per curiam)
(challenging EPA’s reinstatement of the waiver for California’s ACC I program).
223 See Stipulation of Dismissal, Union of Concerned Scientists v. NHTSA, No. 19-1230 (D.C. Cir. July 9, 2024)
(dismissing the case).
224 98 F.4th 288, 314 (D.C. Cir. 2024) (per curiam). The petitioners also argued that EPA’s waiver violated Section
209(b) because California does not “need” its stricter GHG emissions regulations to meet “compelling and
extraordinary circumstances” and that EPCA preempts state GHG standards.
225 78 Federal Register 2112.
226 84 Federal Register 51310.
227
87 Federal Register 14332.
228 Ohio v. EPA, 98 F.4th at 293-294.
229 U.S. Const. amdt. X; CRS, “Equal Sovereignty Doctrine,” Constitution Annotated, https://constitution.congress.gov/
browse/essay/amdt10-4-3/ALDE_00013628/['equal’,%20'sovereignty’], accessed June 11, 2024.
230 Ibid.
231 Ibid.; Nw. Austin Mun. Util. Dist. No. One v. Holder, 557 U.S. 193, 203 (2009); Shelby Cnty. v. Holder, 570 U.S.
529, 544 (2013).
232 Shelby Cnty., 570 U.S. at 557.
233 Ibid. at 537-538.
234 Ibid. at 542 (quoting Nw. Austin, 557 U.S. at 203).
Congressional Research Service
30
California and the Clean Air Act (CAA) Waiver: Frequently Asked Questions
American voter registration rates and turnout in covered jurisdictions no longer justified applying
the preclearance requirement to those jurisdictions.235
The parties challenging Section 209(b) in Ohio v. EPA argued that by granting California more
sovereign authority to regulate than other states enjoy, Congress violated the equal sovereignty
doctrine.236 The D.C. Circuit disagreed, finding that no court had ever applied the equal
sovereignty doctrine to Congress’s exercise of its powers pursuant to the Commerce Clause of the
Constitution.237 The Supreme Court in Shelby County was evaluating Congress’s authority to
regulate elections pursuant to the Fifteenth Amendment to the Constitution.238 Unlike the
Fifteenth Amendment, which permits Congress to enforce its terms through “appropriate
legislation,” the Commerce Clause is a grant of plenary power to Congress.239 In addition, the
Court in Shelby County held that the VRA was a significant intrusion into the states’ traditional
power to regulate elections.240
By contrast, Section 209(b) regulates interstate pollution, which, according to the D.C. Circuit, all
agree falls squarely within Congress’s authority to regulate pursuant to the Commerce Clause.241
Shelby County, the D.C. Circuit held, “does not support requiring a heightened justification for
disparate intrusions into areas over which the Constitution grants Congress such comprehensive
control.”242
Finally, the D.C. Circuit explained, Shelby County did not create a categorical bar against
Congress providing different levels of sovereign authority to different states.243 Rather, Shelby
County held that the equal sovereignty doctrine “required only that Congress show the disparate
treatment is sufficiently related to the problem that it targets.”244 The D.C. Circuit found it
“counterintuitive” for the petitioners to read the Commerce Clause as imposing a categorical bar
on treating states differently when the Commerce Clause grants Congress “primacy over
interstate commerce.”245
On July 2, 2024, industry association petitioners asked the Supreme Court to review the D.C.
Circuit’s decision.246 They argue that the D.C. Circuit’s determination that they lack constitutional
standing to bring a challenge to EPA’s ACC I waiver was wrongly decided and that EPA’s
decision to grant the ACC I waiver was unlawful.247 On July 5, 2024, state petitioners led by Ohio
joined the industry associations in asking the Supreme Court review the D.C. Circuit’s
decision.248 The state petitioners argue that Section 209(b) is unconstitutional because it violates
the equal sovereignty doctrine.249 On December 13, 2024, the Supreme Court agreed to hear the
235 Ibid. at 557.
236 Ohio v. EPA, 98 F.4th 288, 307 (D.C. Cir. 2024).
237 Ibid.
238 Ibid. at 309.
239 Ibid.
240 Ibid.
241 Ibid. at 310.
242 Ibid.
243 Ibid.
244 Ibid.
245 Ibid.
246 Petition for a Writ of Certiorari, Diamond Alternative Energy, LLC. v. EPA, No. 24-7 (U.S. July 2, 2024).
247 Ibid. at I.
248 Petition for a Writ of Certiorari, Ohio v. EPA, No. 24-13 (U.S. July 5, 2024).
249 Ibid. at i.
Congressional Research Service
31
California and the Clean Air Act (CAA) Waiver: Frequently Asked Questions
appeal brought by the industry association petitioners but limited its review to whether the
petitioners have constitutional standing to challenge the waiver on grounds that EPCA preempts
EPA’s authority to grant the waiver and whether the waiver is “consistent” with Section 202(a).250
Were the Court to find in favor of the petitioners, petitioners could revive these claims in the D.C.
Circuit.
Conflicts with the Energy Policy and Conservation Act (EPCA) and
California Regulation of GHGs
Several legal challenges to waivers for GHG emissions have argued that EPCA preempts
California regulations that are “related to fuel economy standards” and that, as a result, EPA
cannot grant a waiver pursuant to Section 209(b). EPCA—which was first enacted in the 1970s
to, in part, improve vehicle fuel efficiency—contains an express preemption provision that
prohibits “a State or political subdivision of a State” from “adopt[ing] or enforc[ing] a law or
regulation related to fuel economy standards ... covered by an average fuel economy standard”
pursuant to EPCA.251 As noted above, the Trump Administration interpreted this language as
prohibiting EPA from issuing a waiver to California pursuant to Section 209(b) because the
Trump Administration believed that GHG emissions standards necessarily affected fuel economy
and accordingly were “related to” fuel economy standards.252
A number of challenges based on this interpretation of EPCA have been brought to EPA waivers
for California GHG emissions standards. Two of the challenges have resulted in decisions on the
merits.253 Both decisions upheld EPA’s authority to grant waivers for GHG emissions standards.254
Both decisions, however, lack any precedential value to bind future court decisions because they
were issued by federal district courts.255
The U.S. District Court for the District of Vermont was the first court to address the potential for
conflict between EPCA and the CAA in Green Mountain Chrysler Plymouth Dodge Jeep v.
Crombie.256 The court held that EPCA did not conflict with or preempt California GHG
regulations that had received a waiver from EPA.257 Analyzing the enactment histories of both
EPCA and Section 209(b), the court noted that just two years after Congress enacted EPCA, it
amended Section 209(b) and was well aware of the relationship between fuel economy and
emissions regulations.258 The House report that accompanied the amendment stated, “The
experience of the stricter California standards shows that tighter standards do not necessarily
mean a fuel economy reduction.”259
250 Order, Diamond Alternative Energy, LLC v. EPA, No. 24-7 (U.S. December 13, 2025). The Court heard oral
argument on April 23, 2025.
251 49 U.S.C. §32919(a).
252 84 Federal Register 51310.
253 See Green Mountain Chrysler Plymouth Dodge Jeep v. Crombie, 508 F. Supp. 2d 295 (D. Vt. 2007); Central Valley
Chrysler-Jeep, Inc. v. Goldstene, 529 F. Supp. 2d 1151 (E.D. Cal. 2007). The petitioners in Ohio v. EPA also raised this
issue, but the D.C. Circuit did not address the merits because the court found that the petitioners lacked constitutional
standing to bring that claim. 98 F.4th 288, 299 (D.C. Cir. 2024).
254 Green Mountain, 508 F. Supp. 2d at 350-357; Central Valley, 529 F. Supp. 2d at 1171-1179.
255 Green Mountain, 508 F. Supp. 2d at 350-357; Central Valley, 529 F. Supp. 2d at 1171-1179.
256 Green Mountain, 508 F. Supp. 2d at 346.
257 Ibid. at 350-357.
258 Ibid. at 346.
259 Ibid. (citing H.R. Rep. No. 95-294, at 301-302 (1977)).
Congressional Research Service
32
California and the Clean Air Act (CAA) Waiver: Frequently Asked Questions
EPCA’s enactment history points in the same direction, the court found. EPCA contains a
provision that requires NHTSA to consider “other motor vehicle standards of the government on
fuel economy” when setting fuel economy standards.260 When EPCA was enacted in 1975, it
explicitly included in the term “other motor vehicle standards” California emissions standards
that received a waiver from EPA.261 The provision that explicitly identified California standards
as “other motor vehicle standards” was ultimately dropped from the statute in 1994 because that
provision dealt with a modification process that applied only to MY1978-MY1980.262 The 1994
recodification, the court found, was not intended to work any substantive change to EPCA.263
Based on this history, the court held that once EPA grants California a waiver, California’s
regulations “become[] a motor vehicle standard of the government, with the same stature as a
federal regulation” that NHTSA must take into consideration when setting fuel economy
standards.264
In Central Valley Chrysler-Jeep Inc. v. Goldstene, the U.S. District Court for the Eastern District
of California similarly held that EPCA did not conflict with or preempt California’s GHG
emissions standards.265 Relying heavily on the Supreme Court’s opinion in Massachusetts v. EPA
and the Green Mountain decision, the court held that EPCA’s provision requiring NHTSA to
consider “other motor vehicle standards of the government on fuel economy” included California
regulations that had received a waiver from EPA pursuant to Section 209(b).266 The court
reasoned that this language in EPCA, instead of preempting California regulations, requires that
NHTSA “harmonize milage standards” with California emissions standards that have been
granted a waiver.267 The court added that this approach is reflected in the Supreme Court’s
discussion of EPCA and the CAA in Massachusetts.268 In Massachusetts, the Court explained that
the purposes of EPCA and the CAA are sufficiently different to permit both statutes to operate
independently.269 Referring to the respective requirements of the CAA and EPCA, the Supreme
Court wrote “[t]he two obligations may overlap, but there is no reason to think the two agencies
cannot both administer their obligations and yet avoid inconsistency.”270
Pending Litigation: Western States Trucking Association, Inc. v. EPA
In April 2023, EPA issued a waiver for California GHG emission control standards for heavy-duty
vehicles that, among other things, require manufacturers to produce and sell increasing
percentages of zero-emission heavy-duty vehicles and “near zero-emission” heavy-duty vehicles
260 Ibid.
261 Ibid.
262 Ibid.
263 Ibid. (citing P.L. 103-272, 108 Stat. 745 (1994)).
264 Ibid. at 347.
265 Central Valley, 529 F. Supp. 2d at 1171-1179.
266 Ibid. at 1173-1174.
267 Ibid.
268 Ibid.
269 Ibid. at 1166.
270 Ibid. (quoting Massachusetts v. EPA, 549 U.S. 497, 532 (2007)).
Congressional Research Service
33
California and the Clean Air Act (CAA) Waiver: Frequently Asked Questions
in California.271 Soon thereafter, trucking industry groups filed a petition for review in the D.C.
Circuit seeking to have the waiver vacated.272
The petitioners raise three main arguments.273 First, they argue that EPA’s decision to issue a
waiver in this case violates the major questions doctrine.274 The major questions doctrine
precludes an agency from exercising regulatory authority over an issue of vast economic or
political significance without clear congressional authorization to do so.275 The petitioners argue
that the CAA does not clearly provide EPA with the authority to authorize California to mandate
vehicle electrification—an issue of vast economic and political importance.276
Second, the petitioners argue that, because waivers issued by EPA must be “consistent” with
Section 202(a) of the CAA, and Section 202(a) does not permit EPA to mandate electric vehicles,
EPA cannot issue a waiver that has the effect of mandating electric vehicles.277
Third, the petitioners argue that the waiver violates Section 209(b)(1)(B), which requires EPA to
deny a waiver if California does not “need” the waiver “to meet compelling and extraordinary
conditions.”278 The petitioners claim that California’s electric-vehicle mandates are aimed at
addressing climate change.279 Climate change, the petitioners assert, is a global phenomenon that
affects California as much as any other place on the planet.280 In addition, any emissions
reductions achieved by California’s regulation, the petitioners argue, will not meaningfully
address the effects of climate change.281
A group of 19 states also challenged EPA’s waiver.282 The state petitioners raise two primary
arguments.283 First, in a nearly identical argument to that raised in Ohio v. EPA discussed above,
they argue that Section 209(b) violates the equal sovereignty doctrine.284 Second, they argue that
the waiver violates Section 202(a)(3)(C).285 As noted above, Section 209(b) requires that in order
271 EPA, “California State Motor Vehicle and Engine Pollution Control Standards; Heavy-Duty Vehicle and Engine
Emission Warranty and Maintenance Provisions; Advanced Clean Trucks; Zero Emission Airport Shuttle; ZeroEmission Power Train Certification; Waiver of Preemption; Notice of Decision,” 88 Federal Register 20688, April 6,
2023.
272 Petition for Review at 2, Western States Trucking Association, Inc. v. EPA (No. 23-1143) (D.C. Cir. June 6, 2023).
273 Initial Brief for Private Petitioners at xx-xxi, Western States Trucking Association, Inc. v. EPA (No. 23-1143) (D.C.
Cir. Nov. 3, 2023) (hereinafter Initial Brief).
274 Initial Brief at 19.
275 West Virginia v. EPA, 597 U.S. 697, 716 (2022). For more information about the major questions doctrine, see CRS
In Focus IF12077, The Major Questions Doctrine, by Kate R. Bowers.
276 Initial Brief at 20.
277 Ibid. at 28.
278 Ibid. at 39.
279 Ibid. at 42-53.
280 Ibid.
281 Ibid.
282 Petition for Review at 2, Iowa v. EPA (No. 23-1144) (D.C. Cir. June 5, 2023). The state petitioners’ challenge was
consolidated with the industry petitioners’ challenge under the caption Western Trucking Association, Inc. v. EPA.
Order at 1, Western States Trucking Association v. EPA (No. 23-1143) (D.C. Cir. June 6, 2023).
283 Brief of Petitioners the States of Iowa, Alabama, Arkansas, Georgia, Indiana, Kansas, Kentucky, Louisiana,
Mississippi, Montana, Nebraska, North Dakota, Ohio, Oklahoma, South Carolina, Utah, West Virginia, and Wyoming
at vi, Western States Trucking Association, Inc. v. EPA (No. 23-1143) (D.C. Cir. Nov. 3, 2023) (hereinafter Brief of
the States).
284 Ibid. at 17-23.
285 Ibid. at 28-38.
Congressional Research Service
34
California and the Clean Air Act (CAA) Waiver: Frequently Asked Questions
for California to receive a waiver, its regulations must be consistent with Section 202(a).286
Pursuant to Section 202(a)(3)(C), EPA cannot impose certain emissions limits for heavy-duty
vehicles sooner than four years after it promulgates the standard.287 The state petitioners argue
that California’s regulations do not provide the four-year lead time required by Section
202(a)(3)(C) and, accordingly, EPA cannot issue a waiver for those regulations unless the
regulations are consistent with Section 202(a).288
In December 2023, the court issued an order holding the case in abeyance until the D.C. Circuit
issues rulings in two other related cases—Ohio v. EPA and Texas v. EPA.289 As discussed above,
the D.C. Circuit rendered an opinion in Ohio v. EPA in April 2024, holding that Section 209(b)
did not violate the equal sovereignty doctrine.290 The court has yet to issue an opinion in Texas v.
EPA.
Author Information
Benjamin M. Barczewski
Legislative Attorney
Emily N. Peterson
Research Librarian
Kathryn G. Kynett
Analyst in Environmental Policy
Disclaimer
This document was prepared by the Congressional Research Service (CRS). CRS serves as nonpartisan
shared staff to congressional committees and Members of Congress. It operates solely at the behest of and
under the direction of Congress. Information in a CRS Report should not be relied upon for purposes other
than public understanding of information that has been provided by CRS to Members of Congress in
connection with CRS’s institutional role. CRS Reports, as a work of the United States Government, are not
subject to copyright protection in the United States. Any CRS Report may be reproduced and distributed in
its entirety without permission from CRS. However, as a CRS Report may include copyrighted images or
material from a third party, you may need to obtain the permission of the copyright holder if you wish to
copy or otherwise use copyrighted material.
286 42 U.S.C. §7521(a).
287 42 U.S.C. §7521(a)(3)(C).
288 Brief of the States at 17-23.
289 Per Curiam Order at 1, Western States Trucking Association, Inc. v. EPA (No. 23-1143) (D.C. Cir. Dec. 21, 2023).
The petitioners in Texas v. EPA, which has already been argued and submitted to the court for a decision, raise the
question of what authority Section 202(a) provides EPA to regulate electric vehicles.
290 98 F.4th 288 (D.C. Cir. 2024).
Congressional Research Service
R48168 · VERSION 4 · UPDATED
35
This is a copy of a public record, reproduced as it was published. It is not legal advice, and it may not be the version a court would rely on. Check the official source before you cite it.