Amicus Curiae Brief — Suncor Energy (U.S.A.) Inc., et al., Petitioners v. County Commissioners of Boulder County, et al.

No. 25-170

In the Supreme Court of the United States

___________________

SUNCOR ENERGY (U.S.A.) INC., et al.,

Petitioners,

v.

COUNTY COMMISSIONERS

OF BOULDER COUNTY, et al.,

Respondents.

___________________

On Writ of Certiorari

to the Supreme Court of Colorado

___________________

BRIEF OF FORMER EPA ADMINISTRATORS,

OFFICIALS, AND SENIOR CAREER STAFF,

AND ENVIRONMENTAL PROTECTION

NETWORK, AS AMICI CURIAE IN SUPPORT

OF RESPONDENTS

___________________

MICHAEL RUBIN

Counsel of Record

CORINNE F. JOHNSON

ALTSHULER BERZON LLP

177 Post Street, Suite 300

San Francisco, CA 94108

(415) 421-7151

mrubin@altber.com

Counsel for Amici Curiae

Mosaic - (301) 927-3800 - Cheverly, MD

49261_Ltrhd.indd

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6/11/08

12:44:0

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TABLE OF CONTENTS

TABLE OF CONTENTS ............................................i

TABLE OF AUTHORITIES ................................... iii

INTEREST OF AMICI CURIAE .............................. 1

SUMMARY OF ARGUMENT .................................. 5

ARGUMENT ............................................................. 7

I. Implied Preemption is Disfavored and

Narrowly Drawn .................................................. 7

II. The Clean Air Act Provides for Robust State

Regulation of Emissions and Does Not Limit

State Regulation of Other Fields ...................... 10

A. National Ambient Air Quality Standards.... 11

B. Stationary Sources ........................................ 12

C. Mobile Sources .............................................. 15

III. Boulder’s State Law Tort Claims Do Not

Interfere with the Clean Air Act’s

Regulation of Emissions. ................................... 17

A. Boulder’s deceptive advertising and

consumer protection claims are not field

preempted ..................................................... 17

B. Boulder’s claims do not conflict with the

Clean Air Act because they do not regulate

emissions ...................................................... 18

C. Any indirect effect that Boulder’s claims

may have on emissions or emitting activity

does not conflict with the Clean Air Act...... 22

CONCLUSION........................................................ 31

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iii

TABLE OF AUTHORITIES

Page(s)

Cases

Am. Elec. Power Co. v. Connecticut,

564 U.S. 410 (2011) ..................................... 13, 24

Cal. Div. of Lab. Standards Enf’t v.

Dillingham Constr., N.A., Inc.,

519 U.S. 316 (1997) ........................................... 26

Chamber of Com. of U.S. v. Whiting,

563 U.S. 582 (2011) ................................... 8, 9, 23

Cipollone v. Liggett Grp., Inc.,

505 U.S. 504 (1992) ....................................... 9, 27

Commonwealth Edison Co. v. Montana,

453 U.S. 609 (1981) ..................................... 25, 26

CSX Transp., Inc. v. Easterwood, 507 U. S.

658, 664 (1993)). .................................................. 9

CTS Corp. v. Waldburger,

573 U.S. 1 (2014) ............................................. 8, 9

Gen. Motors Corp. v. United States,

496 U.S. 530 (1990) ........................................... 10

Int’l Paper Co. v. Ouellette,

479 U.S. 481 (1987) ............... 5, 17, 18, 21, 22, 26

Kansas v. Garcia,

589 U.S. 191 (2020) ................................... 8, 9, 17

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Kurns v. R.R. Friction Prods. Corp.,

565 U.S. 625 (2012) ........................................... 21

Lorillard Tobacco Co. v. Reilly,

533 U.S. 525 (2001) ....................................... 9, 27

Massachusetts v. E.P.A.,

549 U.S. 497 (2007) ..................................... 15, 16

Monsanto Co. v. Durnell,

609 U.S. ___, 2026 WL 1825691 (U.S.

June 25, 2026)...............................................19-20

Motor & Equip. Mfrs. Ass’n, Inc. v. E.P.A.,

627 F.2d 1095 (D.C. Cir. 1979).......................... 15

New York State Conf. of Blue Cross & Blue

Shield Plans v. Travelers Ins. Co.,

514 U.S. 645 (1995) ........................................... 26

Ohio v. E.P.A.,

603 U.S. 279 (2024) ........................................... 10

Oxygenated Fuels Ass’n Inc. v. Davis,

331 F.3d 665 (9th Cir. 2003) ............................. 27

Sierra Club v. Korleski,

681 F.3d 342 (6th Cir. 2012) ............................. 11

Train v. Nat. Res. Def. Council, Inc.,

421 U.S. 60 (1975) ............................................. 12

Union Elec. Co. v. E.P.A.,

427 U.S. 246 (1976) ..................................... 10, 12

Util. Air Regul. Grp. v. E.P.A.,

573 U.S. 302 (2014) ........................................... 10

v

Va. Uranium, Inc. v. Warren,

587 U.S. 761 (2019) ................................ 8, 20, 28

In re Volkswagen “Clean Diesel” Mktg.,

Sales Pracs., & Prods. Liab. Litig.,

959 F.3d 1201 (9th Cir. 2020) ........................... 25

W. Virginia v. E.P.A,

597 U.S. 697 (2022) .......................... 11-14, 23, 24

Whitman v. Am. Trucking Assn’s,

531 U.S. 457 (2001) ........................................... 12

Wyeth v. Levine,

555 U.S. 555 (2009) ............................................. 8

Statutes and Regulations

42 U.S.C.

§§7401 et seq. ..................................................... 19

§7401(a).............................................................. 10

§7401(b).................................................. 10, 23, 27

§7401(c) .............................................................. 11

§§7408–7410 ...................................................... 11

§7411 .................................................................. 12

§7411(d).............................................................. 13

§7411(a).............................................................. 29

§7412 .................................................................. 12

§7412(b).............................................................. 13

§7412(d).............................................................. 14

§7412(f) .............................................................. 14

§7412(l) .............................................................. 14

§7413 .................................................................. 12

§7416 .................................... 14, 15, 17, 20, 23, 27

§7507 .................................................................. 15

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§7521(a).............................................................. 15

§7541(c) .............................................................. 19

§7543(a).............................................................. 15

§7543(b)........................................................ 15, 17

§7604(e) .............................................................. 15

§7671j ................................................................. 19

7 U.S.C.

§136v(b) .............................................................. 20

40 C.F.R.

§63.22 ................................................................. 13

§60.23 ................................................................. 13

§63.90 ................................................................. 14

Cal. Code Regs. tit. 17,

§70200 ................................................................ 12

§70200.5 ............................................................. 12

Other Authorities

80 Fed. Reg. 64662 (Oct. 23, 2015) ......................... 13

89 Fed. Reg. 29440 (Apr. 22, 2024) ........................ 30

89 Fed. Reg. 39798 (May 7, 2024) .................... 29, 30

91 Fed. Reg. 1910 (Jan. 15, 2026) .......................... 30

91 Fed. Reg. 7686 (Feb. 18, 2026) .......................... 16

S. Rep. No. 91-1196 (1970) ............................... 10, 27

H.R. Rep. No. 294 (1977) ....................................... 16

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INTEREST OF AMICI CURIAE1

The individual amici are former Environmental

Protection Agency (“EPA”) administrators, officials,

and senior career staff who have collectively served

across several Republican and Democratic administrations. Together, they have decades of experience

implementing the Clean Air Act and they each remain deeply committed to ensuring that the Act is

properly interpreted and that the Agency’s role in administering the Act remains consistent with congressional intent and historical practice.

Amicus Environmental Protection Network

(“EPN”) is a non-profit organization whose members

include more than 750 former EPA officials and employees, political and non-political appointees alike,

with experience dating back to at least the Carter administration. EPN harnesses the expertise of former

EPA career staff and political appointees who volunteer their time to provide the unique perspective of

former regulators with decades of historical

knowledge and subject matter expertise.

Amici write to share their knowledge of the purpose, structure, and implementation of the Clean Air

Act, the scope of the Agency’s authority under the Act,

and the important role the Act preserves for states in

addressing air pollution. Informed by their deep expertise in EPA’s processes and procedures, amici

share the view that state court deceptive advertising

and consumer protection lawsuits like Boulder’s do

1 No party or counsel for a party authored this brief in whole

or in part, and no person or entity, other than the amici curiae,

their counsel, and the Clean Break Fund, made a monetary contribution to the preparation or submission of this brief.

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not in any way conflict with the purposes of the Act or

EPA’s administration of the Act. The stated purposes

of the Act are to improve air quality and promote public health and welfare through a regime of cooperative

federalism. At no time since the Act’s enactment in

1970 has it been applied or construed as regulating

the fields of truthful advertising or consumer protection that are at issue in this case.

The individual amici, listed alphabetically, are:



Robert Brenner, who served as the Director for the

Office of Policy Analysis and Review in EPA’s Office of Air and Radiation from 1988 through 2011

and concurrently served as Deputy Assistant Administrator in the Office of Air and Radiation from

1999 through 2005. For his work implementing the

Clean Air Act, Mr. Brenner received Presidential

Rank Awards of Distinguished Executive in 2003

and Meritorious Senior Executive Service in 1993

and 1998.



Phillip Brooks, who served as the Director of the

Air Enforcement Division within the Office of Civil

Enforcement in EPA’s Office of Enforcement and

Compliance Assurance from 2011 to 2020.



Jonathan Cannon, who served as EPA’s General

Counsel from 1995 to 1998 and Assistant Administrator for EPA’s Office of Administration and Resource Management from 1993 to 1995. Mr. Cannon also served in senior positions at EPA from

1986 to 1990.



David Dickinson, who served as an Attorney-Advisor within EPA’s Office of Air and Radiation from

1991 to 2025.

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

Robert Dreher, who served as EPA’s Deputy General Counsel from 1997 to 2000 and Senior Advisor

to the General Counsel from 1996 to 1997.



Susmita Dubey, who served as an Attorney in

EPA’s Office of General Counsel from 1993 to 2023,

with 24 years of that time in the Air and Radiation

Law Office.



Alan Eckert, who served at EPA from 1970 to 2004,

including as the Associate General Counsel for the

Air and Radiation Law Office in EPA’s Office of

General Counsel from 1986 to 2002.



Avi Garbow, who served as EPA’s General Counsel

from 2013 to 2017, as well as Deputy General

Counsel from 2009 to 2013 and EPA Senior Counselor to the Administrator in 2021.



Joseph Goffman, who served as Assistant Administrator for EPA’s Office of Air and Radiation from

2024 to 2025, Principal Deputy Assistant Administrator in that office from late 2021 through 2024,

and Acting Assistant Administrator for the remainder of 2021.



John Hannon, who served as an Assistant General

Counsel from 1995 to 2014 and as an Attorney

from 1990 to 1995 in the Air and Radiation Law

Office in EPA’s Office of General Counsel, and as

an Attorney-Advisor in EPA’s Office of Air and Radiation from 1985 to 1990.



Janet McCabe, who served as Deputy Administrator of EPA from 2021 to 2024, Acting Assistant Administrator for EPA’s Office of Air and Radiation

from 2013 to 2017, and Deputy Assistant Administrator of that office from 2009 to 2013.

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

Gina McCarthy, who served as the EPA Administrator from 2013 to 2017, and as Assistant Administrator for EPA’s Office of Air and Radiation from

2009 to 2013.



Kevin McLean, who served as a Deputy Associate

General Counsel from 2005 to 2013, as an Assistant General Counsel from 1995 to 2005, and as an

Attorney from 1990 to 1995 in the Air and Radiation Law Office in EPA’s Office of General Counsel.



David Orlin, who served as an Assistant General

Counsel from 2014 to 2022, and as an Attorney

from 2004 to 2014 in the Air and Radiation Law

Office in EPA’s Office of General Counsel.



Richard Ossias, who served as Associate General

Counsel and Director of the Air and Radiation Law

Office in EPA’s Office of General Counsel from

2005 to 2011, and as Deputy Associate General

Counsel in that office from 1995 to 2005. Mr.

Ossias was also an Attorney with that office from

1980 to 1995.



Bob Perciasepe, who served as EPA Deputy Administrator from 2009 to 2014 and as Assistant Administrator for EPA’s Office of Air and Radiation

from 1998 to 2001.



William Reilly, who served as the EPA Administrator from 1989 to 1993.



Eric Schaffer, who served as Director of the Office

of Civil Enforcement within EPA’s Office of Civil

Enforcement and Compliance Assurance from

1997 to 2002, and Deputy Director of EPA’s Office

of Compliance from 1994 to 1997.

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

Mike Thrift, who served as an Attorney in the Air

and Radiation Law Office in EPA’s Office of General Counsel from 1992 to 2025.



Jan Tierney, who served as an Attorney in the Air

and Radiation Law Office in EPA’s Office of General Counsel from 1990 to 2020.

SUMMARY OF ARGUMENT

Nothing in the text or structure of the Clean Air

Act preempts respondents’ (“Boulder’s”) Colorado

state law tort claims. Preemption of those deceptive

advertising and consumer protection claims—which

are firmly anchored in the state’s traditional police

powers—would seriously encroach upon state sovereignty. Petitioners (“Suncor”) and their amici fall far

short of establishing the requisite clear and manifest

congressional purpose necessary to justify that intrusion.

In arguing otherwise, Suncor and its amici principally attack claims that Boulder does not assert:

claims to “regulate” out-of-state emissions sources. Indeed, their reliance on International Paper Co. v.

Ouellette, 479 U.S. 481 (1987), depends entirely on recasting Boulder’s deception and other tort claims as

efforts to impose emission controls. But Boulder’s

claims seek only to recover money damages for Suncor’s misleading promotional and other tortious conduct relating to the sale of fossil fuel products. Even if

successful, those claims do not seek to, and will not,

impose any emissions controls or limitations on any

sources. Boulder’s claims thus fall far outside any

sphere of regulation covered by the Act, and Ouellette

is inapposite.

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Suncor and its amici’s arguments also badly misconstrue the text, structure, and purposes of the Clean

Air Act. The central purpose of the Act is to reduce air

pollution to protect public health and welfare. Far

from vesting the EPA with exclusive federal control

over all emissions, the Act expressly provides for a significant state role in devising additional mechanisms

for helping to achieve that broad public policy goal. Indeed, every major program under the Act is structured

to permit the EPA to set minimum emission standards or controls, while in most instances authorizing

the states to regulate those same emissions more

stringently. Boulder’s claims, which principally target

Suncor’s allegedly deceptive and tortious sales conduct, pose no obstacle to the statutory goals and structure.

Essentially, Suncor argues that Boulder’s claims

must be found preempted, not because they actually

conflict with the Act, but because they may indirectly

or tangentially affect fossil fuel emissions through an

“attenuated” chain of causation—that is, they may result in a judgment that encourages Suncor voluntarily

to take steps that may lead to fewer emissions from its

products. But a reduction in harmful emissions would

not conflict with the Act’s purposes. Nor would it conflict with EPA’s administration of the Act. While Congress authorized the EPA to set and enforce minimum

federal standards, Congress has never suggested that

the Agency should encourage, let alone require, polluters to emit up to the ceiling set by those standards.

Any reduction in emissions resulting from Boulder’s lawsuit would, in any event, be incidental: Suncor worries that imposing monetary liability against

fossil fuel companies might affect its financial stability and impel it to reduce output of fossil fuel products,

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thereby resulting in lower emissions. But that same

argument could be directed against many other types

of lawsuits against fossil fuel companies, and many

other traditional state regulations as well (such as imposing taxes or minimum wages). It would stretch conflict preemption far beyond any recognized limits to

foreclose state action on that basis.

Suncor and its amici’s final arguments are similarly unavailing. Suncor suggests, without any evidence, that a judgment in Boulder’s favor could disrupt the fossil fuel market. But the Clean Air Act’s

purposes and objectives do not include protecting the

fossil fuel energy market. Suncor also suggests that

lawsuits like Boulder’s will affect EPA’s ability to set

appropriate emissions standards. But the Agency has

always applied the Act against the backdrop of market

uncertainties in regulated industries (including the

possibility that companies may be sued or otherwise

endure financial setbacks) and parallel state regulation. To the extent the impacts of such lawsuits are in

any way relevant to the statutory factors EPA considers when regulating, EPA is amply equipped to take

those impacts into consideration, including through

notice-and-comment rulemaking and its own internal

expertise.

ARGUMENT

I. Implied Preemption is Disfavored and Narrowly Drawn

Although the Clean Air Act contains express

preemption provisions, Suncor and its amici do not

contend that anything in the Act expressly preempts

Boulder’s claims. Instead, they principally assert that

the Act implicitly preempts Boulder’s claims because

those claims purportedly interfere with the Act’s

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purposes and the methods by which EPA pursues

them. Pet. Br. 45; U.S. Br. 28-29. Suncor also makes

the perfunctory argument that the Clean Air Act

preempts the entire field of emissions regulation, Pet.

Br. 44, an argument that Suncor’s amicus United

States does not join.

“The preemption of state laws represents ‘a serious

intrusion into state sovereignty.’” Va. Uranium, Inc.

v. Warren, 587 U.S. 761, 773 (2019) (plurality opinion)

(quoting Medtronic, Inc. v. Lohr, 518 U.S. 470, 488

(1996)). For that reason, “in all preemption cases, and

particularly in those in which Congress has legislated

in a field which the States have traditionally

occupied,” the Court “start[s] with the assumption

that the historic police powers of the States were not

to be superseded by the Federal Act unless that was

the clear and manifest purpose of Congress.” Wyeth v.

Levine, 555 U.S. 555, 565 (2009) (quotation omitted).

The presumption against preemption “has greatest

force … in an area traditionally governed by the

States’ police powers.” CTS Corp. v. Waldburger, 573

U.S. 1, 19 (2014) (plurality opinion).

‘[T]he purpose of Congress is the ultimate

touchstone” of preemption analysis. Wyeth, 555 U.S.

at 565 (quotation omitted). That purpose must be

evident in the statute itself, as it is settled that

“[i]mplied preemption analysis does not justify a freewheeling judicial inquiry into whether a state statute

is in tension with federal objectives.” Chamber of Com.

of U.S. v. Whiting, 563 U.S. 582, 607 (2011) (quotation

omitted). “Invoking some brooding federal interest” is

“never … enough to win preemption of a state law.”

Va. Uranium, 587 U.S. at 767. Rather, “all preemption

arguments[] must be grounded ‘in the text and structure of the statute at issue.’” Kansas v. Garcia, 589

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U.S. 191, 208 (2020) (quoting CSX Transp., Inc. v.

Easterwood, 507 U. S. 658, 664 (1993)).

A “high threshold must be met if a state law is to

be preempted for conflicting with the purposes of a

federal Act.” Whiting, 563 U.S. at 607 (quotation omitted). Where, as here, Congress has enacted specific

provisions that define the preemptive reach of a statute, that affirmative enactment “implies that matters

beyond that reach are not preempted.” Cipollone v.

Liggett Grp., Inc., 505 U. S. 504, 517 (1992). Additionally, field preemption may only be found when “Congress [has] legislated so comprehensively in a particular field that it left no room for supplementary state

legislation.” Kansas, 589 U.S. at 208 (quotation omitted).

Suncor does not meet the “high threshold” of establishing clear and manifest congressional intent to

preempt Boulder’s claims under field or obstacle

preemption. Boulder’s wrongful promotion and other

tort claims are deeply rooted within its traditional

state police powers. See Lorillard Tobacco Co. v.

Reilly, 533 U.S. 525, 541–42 (2001) (advertising); CTS

Corp., 573 U.S. at 19 (nuisance and other torts). The

Clean Air Act regulates emissions of air pollutants,

while Boulder’s claims do not. Boulder’s claims, even

if successful, will not impose any emission controls on

anyone; nor will they result in the state court enjoining petitioners from engaging in any emitting or fossil

fuel activity. But even if Boulder’s claims came close

to regulating emissions, the state court’s adjudication

of those claims would still not conflict with the Act,

which expressly allows for more stringent state regulation of many emissions, including greenhouse gases.

Boulder’s claims are plainly not field preempted

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either, especially given the Act’s express savings

clauses for state action.

II. The Clean Air Act Provides for Robust State

Regulation of Emissions and Does Not Limit

State Regulation of Other Fields

The central purpose of the Clean Air Act is “to protect and enhance the quality of the Nation’s air resources so as to promote the public health and welfare

and the productive capacity of its population.”42

U.S.C. §7401(b)(1); see S. Rep. No. 91-1196 at 1 (1970)

(Clean Air Act’s purpose is “to attack a critical and

growing national problem of air pollution” due to

“deep concern for protection of the health of the

American people”); Union Elec. Co. v. E.P.A., 427 U.S.

246, 256 (1976) (the Act was a “remedy to what was

perceived as a serious and otherwise uncheckable

problem of air pollution”). The Act principally pursues

that goal by “regulat[ing] pollution-generating emissions from both stationary sources, such as factories

and powerplants, and moving sources, such as cars,

trucks, and aircraft.” Util. Air Regul. Grp. v. E.P.A.,

573 U.S. 302, 308 (2014).

Congress recognized that “air pollution prevention

... and air pollution control at its source is the primary

responsibility of States and local governments.” 42

U.S.C. §7401(a)(3). Congress therefore made “the

States and the Federal Government partners in the

struggle against air pollution” under the Act. Gen.

Motors Corp. v. United States, 496 U.S. 530, 532

(1990); see also Ohio v. E.P.A., 603 U.S. 279, 283

(2024) (“The Clean Air Act regulates air quality

through a federal-state collaboration.”) (quotation

omitted). As discussed below, the fundamental structure of every major program under the Act requires

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EPA to set minimum federal emission standards or

controls—that is, standards or controls that set a ceiling for emissions—while generally leaving states (and

often local governments) free to regulate emissions

more stringently. Indeed, another express purpose of

the Act is “to encourage or otherwise promote reasonable … State[] and local governmental actions … for

pollution prevention.” 42 U.S.C. §7401(c).

While the Act preserves broad state authority over

emissions in almost all instances, its plain terms do

not reach beyond that. Nowhere does the Act purport

to limit, or to authorize EPA to limit, traditional state

authority in other areas besides emissions. A brief

survey of the main pollution control programs under

the Act demonstrates both the limited subject matter

of the Act and the substantial role it reserves for the

states.

A. National Ambient Air Quality Standards

The flagship program of the Clean Air Act—the national ambient air quality standards (“NAAQS”) program—is a quintessential example of cooperative federalism. See Sierra Club v. Korleski, 681 F.3d 342, 343

(6th Cir. 2012). Under this program, EPA currently

establishes nationwide air quality standards for six

main pollutants that are emitted “from numerous or

diverse mobile or stationary sources.” W. Virginia v.

E.P.A, 597 U.S. 697, 707 (2022); see 42 U.S.C. §§7408–

7410. A NAAQS designates “the maximum airborne

concentration of [the] pollutant that the public health

can tolerate.” W. Virginia, 597 U.S. at 707 (quotation

omitted). EPA “does not choose which sources must reduce their pollution” or “by how much to meet the ambient pollution target.” Id. That responsibility lies

with the states, which must develop state

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implementation plans to attain the NAAQS within

their state. Id.

States have “considerable latitude” in developing

their plans, and EPA generally has “no authority to

question the wisdom of a State’s choices of emission

limitations.” Train v. Nat. Res. Def. Council, Inc., 421

U.S. 60, 86–87, 79 (1975)). In particular, states may

impose regulations in their plans that are more stringent than required to meet the NAAQS, and EPA is

statutorily required to approve those plans if they

meet the minimum requirements of the federal program. Union Elec., 427 U.S. at 265-66. EPA also cannot disapprove a state plan for being “economically …

infeasible.” Id. The weighing of economic factors is

committed to the states. Whitman v. Am. Trucking

Ass’ns, 531 U.S. 457, 470 (2001) (citing Union Elec.

427 U.S. at 266).

State plans, once approved by EPA, are enforceable as federal law. Union Elec., 427 U.S. at 268; 42

U.S.C. §7413. In addition, states retain authority to

establish their own, state-law ambient standards with

levels, timetables, and implementation requirements

that differ from the federal program’s. See, e.g., Cal.

Code Regs. tit. 17, §§70200, 70200.5 (California’s ambient air quality standards).

B. Stationary Sources

The two main programs by which EPA governs stationary sources are the new source performance

standards program, 42 U.S.C. §7411, and the hazardous air pollutants program, id. §7412. See W. Virginia,

597 U.S. at 707. While EPA performs the primary initial role in developing standards under both programs, the Act explicitly allows states to adopt more

stringent standards.

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1. The new source performance program is the

program through which EPA directly regulates stationary source emissions of NAAQS pollutants and

their precursors, as well as certain other pollutants.

This is the primary program EPA has used to regulate

greenhouse gas emissions from stationary sources.

Am. Elec. Power Co. v. Connecticut, 564 U.S. 410, 424

(2011) (“AEP”). Under this program, EPA identifies

categories of stationary sources that “‘caus[e], or contribut[e] significantly to, air pollution which may reasonably be anticipated to endanger public health or

welfare,’” and it then promulgates federal standards

of performance for new or modified sources in each

category. Id. (alterations in original) (quoting 42

U.S.C. §7411(b)(1)(A)). EPA’s standards must reflect,

after considering a variety of factors including cost,

the amount of emissions limitation “achievable

through the application of the best system of emission

reduction” that EPA determines has been “adequately

demonstrated.” W. Virginia, 597 U.S. at 709 (quoting

42 U.S.C. §7411(a)(1).

This section of the Act also establishes a companion program for existing sources. Once EPA “‘has

set new source standards addressing emissions of a

particular pollutant,’ 80 Fed. Reg. 64711, it must then

address emissions of that same pollutant by existing

sources—but only if they are not already regulated

under the NAAQS or [hazardous air pollutant] programs.” W. Virginia, 597 U.S. at 710. “For existing

sources, EPA issues emissions guidelines, see 40

C.F.R. §§60.22, 60.23 …; in compliance with those

guidelines and subject to federal oversight, the States

then issue performance standards for stationary

sources within their jurisdiction, §7411(d)(1).” AEP,

564 U.S. at 424.

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2. The hazardous air pollutant program targets

toxic pollutants, including substances known or anticipated to be “carcinogenic, …. neurotoxic,” or otherwise “acutely or chronically toxic.” W. Virginia, 597

U.S. at 708 (quoting 42 U.S.C. §7412(b)(2)). For these

pollutants, EPA sets standards that “directly require

all covered sources to reduce their emissions to a certain level.” W. Virginia, 597 U.S. at 708. For major

sources, EPA sets that level by determining the “maximum degree of reduction” it considers “achievable” in

practice by using the best existing technologies and

methods. Id. (quoting 42 U.S.C. §7412(d)(3)). EPA is

required to tighten the standard if necessary to address residual health risks remaining after the technology-based level is implemented. 42 U.S.C.

§7412(f)(2). States may submit plans for implementing and enforcing the federal standards, id. §7412(l),

and, upon approval, those states become authorized to

administer the federal standards, 40 C.F.R. §63.90.

3. Although EPA sets minimum emissions

standards for stationary sources under these two programs, state and local governments retain broad authority to further regulate those emissions and

sources. The Act’s saving clause expressly provides

that state and local governments may impose stricter

regulations on stationary sources, stating that except

as otherwise provided with respect to certain mobile

sources, “nothing … shall preclude or deny the right

of any State or political subdivision thereof to adopt or

enforce (1) any standard or limitation respecting emissions of air pollutants or (2) any requirement respecting control or abatement of air pollution.” 42 U.S.C.

§7416. Only less stringent standards are preempted:

“[I]f an emission standard or limitation is in effect under an applicable implementation plan or under [the

15

hazardous air pollutant or new source performance

standards program], such State or political subdivision may not adopt or enforce any emission standard

or limitation which is less stringent than the standard

or limitation under such plan or section.” Id.2

C. Mobile Sources

EPA establishes emission standards for new motor vehicles with respect to pollutants that EPA has

determined “cause, or contribute to, air pollution

which may reasonably be anticipated to endanger

public health or welfare.” Massachusetts v. E.P.A., 549

U.S. 497, 506 (2007) (quoting 42 U.S.C. §7521(a)(1)).

The Act generally preempts state standards “relating to the control of emissions from new motor vehicles,” 42 U.S.C §7543(a), with one major exception:

The Act permits California to adopt more stringent

emissions standards for new motor vehicles, id.

§7543(b)(1)(B), and allows other states to adopt California’s stricter limits, id. §7507. See Motor & Equip.

Mfrs. Ass’n, Inc. v. E.P.A., 627 F.2d 1095, 1095 (D.C.

Cir. 1979). Specifically, this exception requires EPA to

waive preemption for California’s motor vehicle standards unless it makes certain findings under a highly

deferential standard of review. Motor & Equip. Mfrs.

Ass’n, 627 F.2d at 1095, 1105-12, 1120, 1124. Congress’s intent in creating this exception was to “‘afford

California the broadest possible discretion in selecting

the best means to protect the health of its citizens and

2 In a different savings clause, the Act provides that

“[n]othing in this section [regarding federal citizen suits] shall

restrict any right which any person (or class of persons) may have

under any statute or common law to seek enforcement of any

emission standard or limitation or to seek any other relief.” 42

U.S.C. §7604(e) (emphasis added).

16

the public welfare.’” Id. at 1110 (quoting H.R. Rep. No.

294, 95th Cong., 1st Sess. 301-02 (1977), U.S. Code

Cong. & Admin. News 1977, p.1380).

As a result of this exception, large swaths of the

country had motor vehicle emissions standards that

were more stringent than EPA’s and for which EPA

had issued waivers to California.3 For example, as of

May 2025, 17 states and the District of Columbia had

adopted some subset of California’s standards. See

Cong. Rsch. Serv., R48168, California and the Clean

Air Act (CAA) Waiver: Frequently Asked Questions

(May 9, 2025) at 7, available at https://www.congress.gov/crs-product/R48168. Along with California,

those states accounted for almost 40% of new lightduty vehicle registrations and 25% of new heavy-duty

vehicle registrations in the United States in 2023. Id.

Although this Court held that EPA may regulate

greenhouse gases under the Act’s mobile source program, see Massachusetts, 549 U.S. at 527–35, EPA recently determined that it does not have statutory authority to do so. See 91 Fed. Reg. 7686 (Feb. 18, 2026).

3 For the current status of waivers, see EPA, Vehicle Emissions

California

Waivers

and

Authorizations,

https://www.epa.gov/state-and-local-transportation/vehicleemissions-california-waivers-and-authorizations (last visited

July 27, 2026).

17

III. Boulder’s State Law Tort Claims Do Not Interfere with the Clean Air Act’s Regulation

of Emissions.

A. Boulder’s deceptive advertising and consumer protection claims are not field

preempted

Suncor’s assertion that the Clean Air Act preempts

the entire field of “interstate pollution regulation,”

Pet. Br. 44, rests on the flawed premise that Boulder’s

claims for deceptively advertising and knowingly selling harmful fossil fuel products regulate within that

field. That vast overstatement does not withstand

scrutiny. See infra at 18-20; Kansas, 589 U.S. at 20910 (no field preemption where challenged state law

regulated outside the field of the federal law). Even if

Boulder’s claims could be construed as somehow regulating some aspect of the field of interstate emission

controls (which they do not), it is clear that Congress

has not “legislated so comprehensively” under the Act

that it “left no room for supplementary state” regulation. Kansas, 589 U.S. at 208 (quotation omitted). Far

from retaining exclusive federal control, the Act expressly contemplates and authorizes additional state

regulation beyond EPA’s. See, e.g., 42 U.S.C. §§7416,

7543(b) (savings clauses); supra at 12-16.

Suncor’s reliance on Ouellette, 479 U.S. 481, to contend otherwise is misplaced. Ouellette rejected field

preemption, holding that similar savings clause language in the Clean Water Act “negates the inference

that Congress left no room for state causes of action”

to address interstate water pollution. Id. at 492. Even

under a conflict preemption analysis, Ouellette held

that states affected by out-of-state discharges may

regulate interstate water pollution by enforcing the

18

law of the source state against the discharger—further dooming Suncor’s attempt to rely on Ouellette to

assert field preemption of all interstate pollution. See

id. at 497–98.

B. Boulder’s claims do not conflict with the

Clean Air Act because they do not regulate

emissions

The text and structure of the Act do not demonstrate any congressional intent to foreclose tort claims

like Boulder’s, because there is no conflict between

those claims and the Act’s language and scope. State

tort laws that prohibit defendants from misleading

the public about the dangers of emissions caused by

their products, or from engaging in the knowing production and sale of products on a scale that causes

harmful levels of emissions, clearly do not pose any

obstacle to the Clean Air Act’s central purpose of reducing air pollution in furtherance of promoting public health and welfare.

Nor does state tort law pose any obstacle to the

Act’s statutory methods of achieving that goal by controlling or limiting emissions from sources. Boulder’s

claims target different conduct from the emitting activities regulated by the Clean Air Act. One set of

Boulder’s claims seeks to hold Suncor liable for deceptively marketing its fossil fuel products, including by

failing to warn and intentionally misleading the public about its fossil-fuel products’ role in contributing to

the impacts of climate change. Resp. Br. 4. The second

seeks to hold Suncor liable for “knowingly caus[ing]

and contribut[ing] to the alteration of the climate”

through its production, refining, promotion, and sale

of fossil fuels. Id. Neither set seeks to impose liability

19

for Suncor’s emissions or emitting activities that are

regulated by the Act.

Boulder’s requested remedies do not seek to impose limits on Suncor’s or anyone else’s emissions either. Boulder seeks only monetary relief. JA 137-38. A

favorable verdict would not mandate or require Suncor (or any source regulated by the Act) to reduce

emissions, would not impose any emission controls or

standards, would not modify or affect any permit issued under the Act, would not change any regulations

issued under the Act, and would not require anyone to

produce, sell, use, or consume fewer fossil fuel products.

Boulder’s deceptive marketing claims are particularly far afield from any authority EPA exercises, or

any tasks EPA or states perform, to implement the

Act. See Resp. Br. 49. The Act does not contain any

provisions that enable or require EPA to regulate

product marketing generally, whether with respect to

emissions or otherwise. See supra at 10-17; 42 U.S.C.

§§7401 et seq. The only labeling requirements imposed

by the Act—which are at best a distant cousin to marketing regulation—obligate motor vehicle manufacturers to permanently affix under-hood tags or labels

to new cars or engines certifying compliance with

EPA’s mobile vehicle emissions standards, 42 U.S.C.

§7541(c), and require products containing or manufactured with certain ozone depleting substances to include a label specifying the substance and that it depletes ozone, id. §7671j. Congress plainly knew how to

direct EPA to regulate disclosures and warnings but

generally chose not to do so in the Clean Air Act—let

alone to provide EPA exclusive authority over the

broader arena of marketing. Cf. Monsanto Co. v. Durnell, 609 U.S. ___, 2026 WL 1825691, *2, *5 (U.S. June

20

25, 2026) (Congress vested EPA with exclusive labeling authority under FIFRA by expressly “prohibit[ing]

States from imposing ‘any requirements for labeling

or packaging in addition to or different from those required’” by EPA) (quoting 7 U.S.C. §136v(b)). The promotional conduct at issue in Boulder’s claims falls far

outside the scope of the Act.

Suncor and its amici are unable to identify any specific provision of the Act, or any specific implementation of the Act by EPA, as to which Boulder’s claims

would conflict or pose an obstacle to achieving. Petitioners refer to the new source performance standard

program for stationary sources. Pet. Br. 45; U.S. Br.

29. But even if Boulder’s state law claims actually

sought to regulate a facility’s emissions or emitting activity (which they do not), the Act’s saving clause expressly authorizes states to regulate emissions from

stationary sources more stringently than EPA does.

42 U.S.C. §7416. And clearly, whatever obligations

state law imposes on Suncor with respect to truthful

advertising or consumer protection will not prevent

any regulated stationary sources from achieving compliance with any emissions limitations EPA has set.4

Contrary to the United States’ contention, U.S. Br.

29, 33-34, the fact that Boulder’s claims address “upstream” fossil fuel products does not mean that they

conflict with EPA’s regulation of “downstream” emissions. See Va. Uranium, 587 U.S. at 777–78 (rejecting

argument that state regulation of mining would conflict with Act’s regulation of “later stages of the

4 Amicus United States concedes that the logical consequence

of its position that EPA lacks statutory authority to regulate

greenhouse gas emissions from motor vehicles is that there can

be no conflict with those aspects of the Act. U.S. Br. 34.

21

nuclear fuel life cycle”: “A sound preemption analysis

cannot be as simplistic as that.”). The United States’

argument is not furthered by its citation to Kurns v.

R.R. Friction Prods. Corp., 565 U.S. 625 (2012), see

U.S. Br. 33, because that case dealt with field preemption: the federal statute occupying “the entire field of

regulating locomotive equipment,” including the “design [and] construction … of every part of the locomotive” plainly applied to state law claims against both

manufacturers and railroads. See Kurns, 565 U.S. at

631-32, 636. There is no field preemption issue here.

Suncor and its amici also rely on Ouellette to contend that Boulder’s claims conflict with what they

view as the Act’s implicit preclusion of state regulation of interstate emissions. Pet. Br. 45-46; U.S. Br.

30. Ouellette involved a defendant whose discharges of

pollutants into the waters of one state (the source

state, New York) affected the waters of another (the

affected state, Vermont). 479 U.S. at 483-484. The

plaintiff sued, alleging that those discharges violated

Vermont law. Id. at 484. The Court held that the

Clean Water Act precluded “applying the law of an affected State” to restrict the pollution discharges of “an

out-of-state source.” Id. at 494. The Court reasoned

that holding a New York source liable for violations of

Vermont’s pollution law would “effectively override”

the terms of the Clean Water Act permit that New

York had issued and thus “would undermine the

[Act’s] important goals of efficiency and predictability

in the permit system” by subjecting every source “to a

variety of common-law rules established by the different States along the interstate waterways.” Id. at 49596.

That reasoning is entirely inapplicable. Boulder’s

deceptive advertising and other tort claims do not

22

seek to impose liability on any out-of-state emissions

source for any polluting activities. A judgment in

Boulder’s favor would not override the terms of any

Clean Air Act permit under which any out-of-state

source is operating, nor would it impose any emissions

limitation in any other state. To the contrary, out-ofstate sources would remain subject to the emissions

requirements of their respective states and EPA only.

Thus, even if the Clean Air Act precluded direct state

regulation of interstate emissions, Boulder’s claims

would not implicate that concern.

Even under Ouellette’s reasoning, the Clean Air

Act would not preempt all state regulation of interstate emissions. Ouellette held that the plaintiff remained free to assert claims against the defendant in

Vermont state court under the law of the source state

(New York). 479 U.S. at 498-99. Thus, even if Boulder’s claims regulated interstate emissions, Boulder

would remain free to assert claims under source state

law. Suncor and its amici do not argue that such

claims should be preempted; the Colorado Supreme

Court did not address the issue below; and there has

been no showing or explanation of how any such

preemption argument might or might not appropriately apply to Boulder’s case. Thus, even if Ouellette’s

reasoning were applicable, it would not foreclose Boulder’s case.

C. Any indirect effect that Boulder’s claims

may have on emissions or emitting activity does not conflict with the Clean Air Act

What Suncor and its amici really mean when they

assert that Boulder’s claims “regulate” emissions is

that they believe that Boulder’s lawsuit, if successful,

could indirectly and through what they describe as a

23

very “attenuated” chain of causation eventually result

in less fossil fuel production and sales by Suncor and

others and, therefore, correspondingly reduced emissions of some of the pollutants EPA regulates. Pet. Br.

31, 36; U.S. Br. 32. That possibility—even if later

borne out—provides no basis for finding that the Act

preempts these state tort claims.

1. Suncor and its amici do not identify a single provision of the Act pertaining to EPA’s regulation of

greenhouse gases with which a reduction in emissions

would conflict. Under the Act, EPA sets and enforces

standards that set a ceiling for emissions. Supra at 1016. EPA has no interest in—and certainly is not

charged with—ensuring or encouraging polluters to

emit up to the full extent of that ceiling. The purpose

of the Act, after all, is to reduce emissions to protect

public health. 42 U.S.C. §7401(b)(1). States and local

governments are therefore expressly authorized to require reductions in emissions below the ceiling set by

EPA. Id. §7416. Any reduction that may be a collateral

consequence of Boulder’s lawsuit would be fully consistent with the purposes, objectives, and EPA’s administration of the Act. See Whiting, 563 U.S. at 606

(rejecting argument that stricter state regulation was

implicitly preempted because it would upset the “balance” struck by federal regulation).

In contending otherwise, Suncor and its amici misconstrue the Act as charging EPA with the responsibility to determine the optimum level of pollution for

society in general, such that the purposes and administration of the Act are hindered whenever state action results in fewer fossil fuel product sales or in

fewer emissions than the maximum allowed by EPA.

But this Court recently rejected the argument that

under the Clean Air Act “Congress implicitly tasked

24

[EPA], and [EPA] alone, with balancing the many vital considerations of national policy implicated in deciding how Americans will get their energy.” W. Virginia, 597 U.S. at 729–30 (rejecting argument that

AEP, 564 U.S. 410, confers that power on EPA). Then

as now, “[t]here is little reason to think Congress assigned such decisions to the Agency.” Id.

Suncor’s arguments, if accepted, would also

preempt many state laws and lawsuits that have

never before been thought to conflict with the Act,

even though the elements of those claims involve air

pollution emissions—including, for instance, false advertising claims for misrepresenting emissions from

cars or for claiming a fuel product burns cleaner and

does not contribute to traditional air pollution. See,

e.g., AG Paxton: Texas to Receive $50 Million in Judgment against Volkswagen (Nov. 18, 2016) (Texas obtained $50 million in penalties and permanent injunction under Texas Deceptive Trade Practices Act

prohibiting car manufacturer from “misrepresenting

car emissions” or “falsely representing its cars are environmentally friendly”).5

2. Any reduction in interstate emissions tied to

Boulder’s claims would be highly indirect, as a secondary or tertiary effect of the lawsuit (if any). Suncor’s

insistence that Boulder’s lawsuit will “limit interstate

greenhouse gas emissions” is predicated on the notion

that imposing monetary liability on petitioner

5 Available at https://www.texasattorneygeneral.gov/news/releases/ag-paxton-texas-receive-50-million-judgment-againstvolkswagen (linking to In re Volkswagen Clean Diesel Litigation:

Consumer Cases, No. D-1-GN-16-000449 (353 Dist. Ct., Travis

County, Tex. Nov. 17, 2016), Agreed Final Judgment and Permanent Injunction)).

25

companies will affect their financial bottom lines, to

which they may respond by producing fewer fossil fuel

products, which may in turn result in fewer greenhouse gas emissions (assuming other fossil fuel companies do not fill the gap). Pet. Br. 37-38.

But there are many ways in which states can exercise their traditional police power that will affect fossil

fuel companies’ operations or finances and thus induce the companies to make business decisions that

could reduce the output of products produced or sold.

For instance, state or local governments can impose

taxes or minimum wages that directly affect fossil fuel

refineries, powerplants, and companies’ fiscal outlook.

Lawsuits under state law can impose significant monetary liability on fossil fuel companies under personal

injury or workplace safety claims, shareholder suits,

consumer protection or fraud claims, or environmental claims. States and local governments can provide

incentives for wind and solar energy development or

impose renewable portfolio standards on utilities that

reduce demand for fossil fuel companies’ fossil fuels.

The potential or even intention that such state law actions might have some effect on fossil fuel companies’

choices to market, produce, and sell fossil-fuel emitting products (including in other states) does not

transform them into obstacles to the Act’s regulation

of greenhouse gases or other emissions. See, e.g., In re

Volkswagen “Clean Diesel” Mktg., Sales Pracs., &

Prods. Liab. Litig., 959 F.3d 1201, 1206 (9th Cir. 2020)

(rejecting argument that conflict preemption applied

because state penalties for car dealers installing devices that tampered with emissions systems “may result in the imposition of unexpected (and enormous)

liability on [the company]”), cert denied, 142 S.Ct. 521

(2021); see also Commonwealth Edison Co. v.

26

Montana, 453 U.S. 609, 636 n.22 (1981) (state tax on

coal not preempted because the “Clean Air Act does

not mandate the use of coal; it merely prescribes

standards governing the emission[s] … when coal is

used).

This Court has rejected arguments that indirect

economic effects on regulated or even preempted subjects are sufficient to establish federal preemption,

even under statutes like ERISA that have broad express preemption clauses. See, e.g., New York State

Conf. of Blue Cross & Blue Shield Plans v. Travelers

Ins. Co., 514 U.S. 645, 655, 659–60 (1995) (state statute that had an “indirect economic effect on choices

made by insurance buyers, including ERISA plans”

was not preempted, even though ERISA preempts all

state laws that “relate to any employee benefit plan”)

(quotation omitted); Cal. Div. of Lab. Standards Enf’t

v. Dillingham Constr., N.A., Inc., 519 U.S. 316, 334

(1997) (no ERISA preemption where the challenged

statute “alters the incentives, but does not dictate the

choices, facing ERISA plans”).

The deceptive marketing and products liability

conduct at issue in Boulder’s claims is similarly remote from any regulation of emissions that the Clean

Air Act vests in EPA or the states. While Suncor and

its amici rely on Ouellette to contend that direct state

regulation of out-of-state sources should be

preempted, nothing in Ouellette—or, more importantly, in the Clean Air Act—indicates that such

preemption should reach so broadly as to sweep in

state activities that merely indirectly affect emissions

in other states. Quite the opposite is true. The Act’s

express preemption provisions are narrowly focused

on direct emission controls—for example, in the case

of stationary sources, applying only to “any [state]

27

standard or limitation respecting emissions” that is

“less stringent” than EPA’s, 42 U.S.C. §7416—thereby

indicating that state action outside that scope is not

preempted. Cipollone, 505 U.S. at 517; see also Lorillard, 533 U.S. at 541 (“an express definition of the

pre-emptive reach of a statute ... supports a reasonable inference ... that Congress did not intend to preempt other matters”) (quotation omitted).

3. Suncor also suggests that a judgment in Boulder’s favor could disrupt the fossil fuel market. Pet.

Br. 38. That is conjecture at best, fearmongering at

worst. At any rate, Suncor offers no support for its implicit assertion that the Clean Air Act’s purposes and

objectives include ensuring a smoothly functioning

fossil fuel market and cheap fossil fuel products—or

protecting the fossil fuel energy market over others.

See Oxygenated Fuels Ass’n Inc. v. Davis, 331 F.3d

665, 673 (9th Cir. 2003) (state ban of fuel additive

MTBE not preempted, despite alleged effect on gasoline prices, because “a smoothly functioning market

and cheap gasoline” are not a “goal” of the Clean Air

Act).6 The central, stated purpose of the Act is to reduce air pollution. 42 U.S.C. §7401(b). Merely assuming, as Suncor does, “that Congress might not have

wanted to cause a substantial increase in … prices is

not the same as saying that assuring inexpensive gasoline was a goal of the Act.” Oxygenated Fuels Ass’n,

331 F.3d at 673. The Supremacy Clause cannot “be deployed … to elevate abstract and unenacted legislative

6 See also S. Rep. No. 91-1196 at 2 (“The protection of public

health … will require major action throughout the Nation. Many

facilities will require major investments in new technology and

new processes. Some facilities will need altered operating procedures or a change of fuels. Some facilities may be closed.”).

28

desires above state law.” Va. Uranium, 587 U.S. at

777–78.

4. Suncor and its amici contend that Boulder’s lawsuit will disrupt EPA’s ability to set emissions standards for greenhouse gases and may result in standards that are somehow “miscalibrated.” U.S. Br. 29,

34. But EPA’s regulations are intended to achieve

emissions reductions that protect public health and

welfare while considering numerous factors specified

in the statute. See supra at 10-16. The Agency has always been required to apply those statutory factors

against the backdrop of market uncertainties in regulated industries—including the complexities of technological innovation; new information and understanding; the prospect that regulated entities may be

sued, may endure financial challenges, may be surpassed by others, may go bankrupt; or be subject to

other vicissitudes of business—as well as the impacts

of parallel state regulation. To the extent such uncertainty has any relevance to EPA’s statutory duties,

the Agency can account for it through the rulemaking

process, which operates to gather the information relevant to its decision-making. For example, notice and

comment procedures allow stakeholders to identify

any information they believe may bear on the factors

Congress has directed EPA to consider. The Agency

also has considerable information-gathering and analytical capabilities of its own. EPA is well equipped to

address any real-world uncertainty or impacts caused

by Boulder’s lawsuit, to the extent they bear on EPA’s

statutory charges. EPA can also conduct a new notice

and comment rulemaking if facts or circumstances

change in substantial, legally relevant ways.

Boulder’s lawsuit is unlikely to have any relevance

to the factors that EPA is directed to consider, let

29

alone to interfere with EPA’s ability to consider those

factors when regulating emissions. For instance, with

respect to new source performance standards, EPA is

directed to consider, among other factors, the cost to

affected sources of achieving the emission reduction.

See 42 U.S.C. §7411(a)(1). The technology and cost to

achieve an emission standard are unrelated to the potential for legal damages for misleading consumers.

While, as explained above, EPA has the capability, in

an appropriate situation, to consider market uncertainties or economic conditions in an industry when

issuing emission regulations, that does not mean

every external factor that may affect an applicable

market (let alone individual companies) is relevant to

rulemaking—let alone that such external factors,

whether due to a lawsuit or otherwise, interfere with

EPA’s ability to regulate for preemption purposes.

Even if Boulder’s lawsuit were eventually decided

against Suncor, EPA’s duty and ability to consider the

technology and costs of achieving certain standards

(and, to the extent appropriate, any relevant market

conditions) would be unaffected.

The history of EPA’s actions bears this out. During

the pendency of Boulder’s lawsuit, EPA has issued

many regulations in which it had no reason to consider Boulder’s lawsuit and accordingly did not consider it—or any similar lawsuit or potential legal liability for affected industries—in exercising its

statutory duty to consider the costs of a proposed

emission reduction. For example, in May 2024, EPA

promulgated final rules that imposed greenhouse gas

emissions reductions on new and existing fossil-fuelfired electric generating units. See 89 Fed. Reg. 39798

(May 7, 2024). Despite these rules’ obvious regulatory

effects on the oil and gas industry in addition to the

30

electric power generation industry, EPA appropriately did not mention or consider Boulder’s lawsuit (or

any other potential legal liability facing an affected industry) when it reported the costs and benefits of the

rules. See id. at 40004–20.

Similarly, in January 2026, EPA promulgated revised emission standards for stationary combustion

and gas turbines. See 91 Fed. Reg. 1910 (Jan. 15,

2026). Although EPA acknowledged that the rule

would apply to entities in the oil and gas extraction,

electric power generation, and natural gas distribution sectors, see id. at 1911, EPA appropriately did not

mention or consider the Boulder lawsuit (or any other

potential legal liability facing an affected industry)

when it balanced the rule’s costs and benefits. See id.

at 1962–65.

In April 2024, EPA issued a final rule regulating

greenhouse gas emissions from heavy duty vehicles

(such as trucks and buses), in which EPA considered

best estimates of future fuel costs, future costs of electricity, and the cost of State excise taxes. See 89 Fed.

Reg. 29440, 29461 (Apr. 22, 2024). Despite extended

consideration of potentially relevant direct and indirect costs, there was no consideration of costs that

might result from pending lawsuits. See id. at 29631–

54.

In sum, in amici’s many years of experience, they

are not aware of any EPA regulation under the Clean

Air Act that has turned on the potential extrinsic legal

liability of individual regulated entities that arose

from an unrelated area of law—or of any reason to

think that EPA could not consider and address the impacts of claims like Boulder’s if appropriate to do so.

Extending preemption to foreclose such state lawsuits

31

would go far beyond anything contemplated by Congress or the Act.

CONCLUSION

The Colorado Supreme Court’s judgment should be

affirmed.

Respectfully submitted,

MICHAEL RUBIN

Counsel of Record

CORINNE F. JOHNSON

ALTSHULER BERZON LLP

177 Post Street, Suite 300

San Francisco, CA 94108

(415) 421-7151

mrubin@altber.com

cjohnson@altber.com

Attorneys for Amici Curiae Former EPA Administrators, Officials, and Senior Career Staff,

and Environmental Protection

Network

August 3, 2026