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

___________

AMICUS CURIAE BRIEF OF

THE BUCKEYE INSTITUTE

IN SUPPORT OF PETITIONERS

___________

ROBERT ALT

ANDREW M. GROSSMAN

THE BUCKEYE

Counsel of Record

BENJAMIN D. JANACEK

INSTITUTE

88 East Broad Street, CALEB ACKER

Suite 1300

BAKER & HOSTETLER LLP

Columbus, OH 43215 1050 Connecticut Ave., N.W.

(614) 224-4422

Washington, D.C. 20036

robert@buckeyeinsti(202) 861-1697

tute.org

agrossman@bakerlaw.com

Counsel for the Amicus Curiae

i

TABLE OF CONTENTS

TABLE OF AUTHORITIES ...................................... ii

IDENTITY AND INTEREST OF THE AMICUS

CURIAE ....................................................................1

INTRODUCTION AND SUMMARY OF

ARGUMENT.............................................................2

ARGUMENT ...............................................................3

I. Boulder’s Lawsuit Seeks a Damages Remedy

Tantamount to a De Facto Carbon Tax ..................3

A. The Damage Awards Sought in Lawsuits Like

This One Are Tantamount to Damaging Carbon

Taxes……………………………………………….. 4

B. The Relief Sought Here Is a Tax in All But

Name……………………………………………….. 9

II. Boulder’s De Facto Carbon Tax Is Unlawful on

Multiple Grounds .................................................10

A. This Lawsuit Seeks to Impose an

Unconstitutional Extraterritorial Tax .............11

B. Boulder’s Carbon Tax Interferes with Federal

Constitutional Prerogatives to Set Foreign

Policy………….. .................................................14

CONCLUSION ..........................................................22

ii

TABLE OF AUTHORITIES

Cases

Page(s)

Allied-Signal, Inc. v. Dir., Div. of Tax’n,

504 U.S. 768 (1992) ................................... 12, 13, 14

Am. Ins. Ass’n v. Garamendi,

539 U.S. 396 (2003) .............................. 18-19, 20, 21

ASARCO Inc. v. Idaho State Tax Comm’n,

458 U.S. 307 (1982) ............................................... 14

Barclays Bank PLC v. Franchise Tax Bd. of California,

512 U.S. 298 (1994) ......................................... 12, 15

Bos. Stock Exch. v. State Tax Comm’n,

429 U.S. 318 (1977) ......................................... 11, 19

Complete Auto Transit, Inc. v. Brady,

430 U.S. 274 (1977) ......................................... 12, 15

Container Corp. of Am. v. Franchise Tax Bd.,

463 U.S. 159 (1983) ......................................... 11, 15

Fuld v. Palestine Liberation Org.,

145 S. Ct. 2090 (2025) ........................................... 11

Gibbons v. Ogden,

9 Wheat. 1, 6 L.Ed. 23 (1824) ............................... 19

Healy v. Beer Inst., Inc.,

491 U.S. 324 (1989) ............................................... 11

Hencely v. Fluor Corp.,

608 U.S. __, 146 S. Ct. 1086 (2026) ...................... 19

Hines v. Davidowitz,

312 U.S. 52 (1941) ................................................. 19

iii

Int’l Paper Co. v. Ouellette,

479 U.S. 481 (1987) ............................................... 18

Massachusetts v. EPA,

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

MeadWestvaco Corp. ex rel. Mead Corp. v. Ill. Dep’t

of Revenue,

553 U.S. 16 (2008) ........................................... 11, 13

Miller Brothers Co. v. Maryland,

347 U.S. 340 (1954) ............................................... 13

N. Carolina Dep’t of Revenue v. The Kimberley Rice

Kaestner 1992 Fam. Tr.,

588 U.S. 262 (2019) ............................................... 12

Nat’l Pork Producers Council v. Ross,

598 U.S. 356 (2023) .......................................... 11-12

Nelson v. Sears, Roebuck & Co.,

312 U.S. 359 (1941) ................................................. 9

NFIB v. Sebelius,

567 U.S. 519 (2012) ........................................... 9, 10

S. Dakota v. Wayfair,

585 U.S. 162 (2018) ......................................... 13, 14

United States v. Belmont,

301 U.S. 324 (1937) ............................................... 19

United States v. New York,

No. 1:25-cv-03656 (S.D.N.Y.) ................................ 18

United States v. Vermont,

No. 2:25-cv-00463 (D. Vt.) ..................................... 18

Watson v. Emp’s Liability Assurance Corp.,

348 U.S. 66 (1954) ................................................. 12

iv

Zschernig v. Miller,

389 U.S. 429 (1968) ............................................... 19

Statutes

42 U.S.C. § 7410 ....................................................... 18

42 U.S.C. § 7411 ....................................................... 18

42 U.S.C. § 7416 ....................................................... 18

42 U.S.C. § 7521 ....................................................... 18

Other Authorities

Bill Schuette, Courtroom Carbon Tax: How Climate

Lawsuits Pick Your Pocket at the Pump,

Washington Examiner (May 11, 2026) .................. 6

Can State Courts Set Global Climate Policy,

The Federalist Society (Oct. 8, 2025) ................. 4-5

Citizens’ Climate Lobby,

Why Put a Price on Carbon? .................................. 5

Executive Order 14260 (Apr. 8, 2025) .................... 16

Joint Statement by Secretary of State Rubio, Secretary of Energy Wright, and Secretary of Transportation Duffy (Oct. 10, 2025) ................................. 17

Jonathan Zasloff, The Judicial Carbon Tax: Reconstructing Public Nuisance and Climate Change,

55 UCLA L. Rev. 1827 (2008) ................................. 5

Rea S. Hederman Jr., Sai C. Martha, and Aswin

Prabhakar, Damaging Consequences: The

v

Economic Impact of a Federal Carbon Tax,

The Buckeye Institute (Apr. 14, 2026) ......... 5-6, 7-8

United Nations Framework Convention on Climate

Change,

May 9, 1992, S. Treaty Doc. No. 102-38, 1771

U.N.T.S. 107 ..................................................... 15-16

1

IDENTITY AND INTEREST OF

THE AMICUS CURIAE 1

The Buckeye Institute was founded in 1989 as a

nonpartisan independent research and educational

institution—a think tank—to formulate and promote

free-market policy in the States. The Buckeye Institute performs and publishes timely and reliable research on key policy issues, compiling and synthesizing data, formulating free-market policies, and marketing those policy solutions for implementation in

Ohio and replication across the country. Its Economic

Research Center is renowned for the cutting-edge economic models that allow it to analyze the dynamic impacts of policy proposals at the state and federal levels. The Buckeye Institute also files lawsuits and submits amicus briefs to further its mission.

The Buckeye Institute’s interest in this case is

based on its economic analysis of the remedies sought

in lawsuits like this one. Buckeye has long opposed

carbon taxes for the injuries they would inflict on the

U.S. economy, job creation, and economic growth and

dynamism. As Buckeye’s research shows, moneydamages remedies for carbon emissions are economically equivalent to a tax and threaten all the same

consequences.

1 In accordance with Rule 37.6, counsel for the amicus curiae certifies that no counsel for any party authored this brief in whole

or in part and that no person or entity other than the amicus

curiae, its members, or its counsel made a monetary contribution

intended to fund the brief’s preparation or submission.

2

INTRODUCTION AND

SUMMARY OF ARGUMENT

This is not an ordinary tort suit. Instead, it is an

attempt to wield state law to impose a surcharge on

the worldwide production and marketing of fossil

fuels. In economic terms, that is a tax. And that

should inform the Court’s legal analysis. Federalism

principles generally deny states the power to tax outside their territories, much less in foreign lands, no

matter the label that a state slaps on such an exaction. And a global carbon tax, as the City of Boulder

and surrounding County seek to impose here, threatens severe economic consequences for workers, consumers, and ultimately the Nation as a whole. The

same doctrines that forbid a city or state from setting

federal tax policy should also doom this attempt to

achieve the same end through the back door.

The Buckeye Institute’s dynamic economic scoring

model demonstrates how Boulder’s climate nuisance

claims, and similar suits brought by other state and

local governments, seek to impose a carbon tax in purpose and effect. Indeed, as plaintiffs’ counsel recently

admitted, it has long been climate activists’ strategy

to impose backdoor carbon taxes—taxes that they are

incapable of imposing through the normal legislative

process—through these nuisance lawsuits. It is no

surprise then that this lawsuit’s remedy would be tantamount to a carbon tax, both in economic terms and

under this Court’s functional approach to identifying

taxes.

3

A nationwide carbon tax like the one Boulder seeks

to introduce through Colorado law inherently exceeds

its powers under state law and intrudes on exclusive

federal powers in almost every imaginable way. This

brief focuses on two.

First, the remedy sought in this suit runs afoul of

constitutional restrictions on states’ extraterritorial

regulation, including especially through the imposition of liability under taxing schemes or otherwise.

Second, Boulder’s global carbon tax tramples over

the President’s constitutional prerogative to set—as

he has pursuant to congressional delegation—the

United States’ policy on global carbon taxes.

For these reasons, and those canvassed in the Petitioners’ brief, the decision below authorizing Colorado

to reach, regulate, and tax beyond its borders should

be reversed.

ARGUMENT

I.

Boulder’s Lawsuit Seeks To Impose a De

Facto Carbon Tax

Having failed to achieve a carbon tax through the

normal legislative process, plaintiffs have resorted to

the courts in an attempt to impose through fiat what

they cannot accomplish through persuasion. It is no

surprise then that Boulder’s public-nuisance action

against energy producers looks nothing like a conventional attempt to recover for discrete injuries. As the

economic evidence demonstrates—and as Boulder

County’s own counsel recently admitted—the lawsuit

is structured and intended to impose a large,

4

policy-driven tax on the production and consumption

of fossil fuels to alter energy producers’ behavior and

finance plaintiffs’ climate objectives. In economic substance and practical effect, this lawsuit, and those like

it, seeks a result much like a carbon tax.

Rather than seek compensation calibrated to specific local harms, Boulder seeks massive, aggregate

monetary relief untethered from individualized causation. Boulder’s scheme is designed to reshape the

State’s—and ultimately the Nation’s—energy economy, in direct conflict with federal policy. This lawsuit’s structure represents a de facto carbon tax in

purpose and effect: It imposes an across-the-board financial liability on a particular category of economic

activity, which in turn raises energy prices, reduces

investment, changes behavior, and contracts overall

economic output. The Buckeye Institute’s modeling

confirms that climate nuisance litigation operates in

precisely this manner and would severely injure the

United States economy. Of course, as plaintiffs’ counsel has admitted, pushing fossil fuel producers into

bankruptcy is plaintiffs’ ultimate goal.

A. The Damage Awards Sought in

Lawsuits Like This One Are

Tantamount to Damaging Carbon

Taxes

The Buckeye Institute’s economic analysis and

modeling demonstrate that large-scale climate nuisance litigation operates identically to a carbon tax,

with all the damaging consequences of a carbon tax.

That should be unsurprising, since plaintiffs’ counsel

recently said the quiet part out loud, noting plaintiffs’

legal strategy amounts to “an indirect carbon tax,”

5

with the ultimate goal of forcing fossil fuel producers

to “declar[e] bankruptcy.” Can State Courts Set

Global Climate Policy, The Federalist Society, at

32:55-34:43 (Oct. 8, 2025) (comments of David Bookbinder). 2 Plaintiffs’ counsel is not the only climatenuisance advocate to make such an admission. Nearly

twenty years ago, Jonathan Zasloff, a UCLA Professor, wrote that nuisance litigation “has promise because…it essentially becomes a carbon tax—precisely

the instrument that…is routinely dismissed as politically unfeasible. The difference is that it is judicially,

not legislatively, imposed.” Jonathan Zasloff, The Judicial Carbon Tax: Reconstructing Public Nuisance

and Climate Change, 55 UCLA L. Rev. 1827, 1827

(2008). Following failed attempts to impose carbon

taxes and other anti-energy policies through the political process, plaintiffs’ nuisance litigation represents the latest effort of climate activists to implement their preferred policy—this time through litigation rather than legislation.

Climate activists represent net-zero can be achieved

with a roughly $800 billion carbon tax. Citizens’ Climate Lobby, Why Put a Price on Carbon? 3 Nuisance

litigation is the latest attempt to achieve this $800

billion carbon tax, as “awarded nuisance damages

would effectively impose a backdoor carbon tax, which

will raise business and energy costs and ultimately

mean higher prices for goods and services for American families.” Rea S. Hederman Jr., Sai C. Martha,

and Aswin Prabhakar, The Buckeye Institute,

Available at https://fedsoc.org/events/can-state-courts-setglobal-climate-policy.

2

3 Available at https://citizensclimatelobby.org/price-on-carbon/.

6

Damaging Consequences: The Economic Impact of a

Federal Carbon Tax (Apr. 14, 2026). 4 Indeed, nuisance suits in states around the country today are actively seeking hundreds of billions of dollars. Bill

Schuette, Courtroom Carbon Tax: How Climate Lawsuits Pick Your Pocket at the Pump, Washington Examiner (May 11, 2026). 5

Using its proprietary dynamic economic model

STELA (state tax and economic long-run analysis),

The Buckeye Institute has modeled the impacts on

the American economy if plaintiffs and their allies

could successfully use nuisance litigation to achieve

their ultimate goal of net-zero carbon emissions. See

Hederman et al., supra. STELA was calibrated using

publicly available federal data and relied on a “similar

dynamic scoring framework used by federal agencies

to evaluate federal tax proposals.” Id. at 10. The

Buckeye Institute calibrated STELA to “predict how

court-imposed climate-related damages and a national carbon tax will affect GDP, employment, tax

revenue, consumption, and investment at the national level.” Id. 6

Available at https://www.buckeyeinstitute.org/library/docLib/2026-04-14-Damaging-Consequences-The-Economic-Impact-of-a-Federal-Carbon-Tax-policy-report.pdf.

4

Available at https://www.washingtonexaminer.com/opeds/4560949/carbon-tax-climate-lawsuits-gas-prices/.

5

6 STELA has undergone a double-blind peer review and incorpo-

rated comments from those reviews consistent with current academic standards and methodologies. A full technical description

of STELA, which allows researchers to independently validate

STELA’s accuracy and the authors’ conclusions may be found in

Hederman, et al., supra at Apps. A & B.

7

The Buckeye Institute used STELA to model the

economic effects that Coloradans would suffer from

climate nuisance suits. Though many climate nuisance suits do not specify a specific damages figure,

one recent suit, County of Multnomah v. ExxonMobil,

sought over $50 billion in damages for supposed climate-related harms. Buckeye used this proposed figure 7 to dynamically score how damages or abatements on a similar scale would impact the Colorado

economy. First, Buckeye took the per capita damages

from County of Multnomah and adjusted them by the

ratio of per capita incomes between Multnomah

County and Colorado. Buckeye then input that figure

into STELA as an equivalent hypothetical corporate

tax on Colorado’s economy, which the model then used

to estimate changes to GDP, investment, consumer

spending, and employment. STELA’s results were

eye-popping: Colorado’s GDP would decrease by

$537.4 billion (2024 dollars); investment would decline by $317.8 billion; consumer spending would fall

by $86.5 billion; and the state would lose 642,000 jobs.

The Buckeye Institute has also deployed STELA to

model the impact of a hypothetical $800 billion annual carbon tax, which is the ultimate goal of climate

nuisance suit activists. Specifically, STELA modeled

“the economic effects of a court-ordered abatement of

carbon emissions, using an $800 billion annual carbon

tax as an effective proxy.” See Hederman et al., supra,

at 7. The model’s conclusions were stark: “In 2027,

GDP would decrease by $980.4 billion (2024 dollars);

7 The Buckeye Institute’s use of Multnomah County’s alleged

damages in no way endorses the accuracy of that plaintiff’s damages estimate.

8

investment would decline by $385.8 billion; consumer

spending would fall by $378.4 billion; and the economy would shed two million jobs. On a per capita basis, every American would bear nearly $2,900 in lost

economic output.” Id. Modeling the consequences further in time tells a similar story: “By 2034, annual

GDP losses would grow to $1.2 trillion, investment

would decline by $470.0 billion, consumer spending

would fall by $483.8 billion, and 2.4 million jobs would

be lost, as the sustained tax burden compounds across

the country.” Id. These outcomes would devastate the

energy sector. Which, of course, is the entire point of

these nuisance suits: achieve through the courts what

plaintiffs and their allies cannot achieve through

their representatives.

Further, all of these outcomes are indistinguishable

from a carbon tax in a number of salient ways. First,

like a carbon tax, nuisance suit damages attach a

compulsory financial cost to carbon-based energy,

making it more expensive for producers to produce

and consumers to consume. Second, like a carbon tax,

these damages would be awarded as a result of the

otherwise lawful production and sale of fossil fuels,

awarding damages based on the producers’ supposed

aggregate contribution to global climate change.

Third, like a carbon tax, many of these increased costs

will have to be passed on to consumers if energy companies want to survive and remain profitable. Finally,

like a carbon tax, the goal of these lawsuits is to

change behavior – i.e., to first limit and then ultimately eliminate the production of fossil fuels.

9

B. The Relief Sought Here Is a Tax in All

But Name

As discussed above, a money-damages nuisance

remedy for fossil-fuel production is economically

equivalent to a tax. It also resembles one in legal

terms. All the key elements of a tax—compulsory financial cost for carbon-based energy, money paid for

otherwise lawful conduct, and costs passed on to consumers—mean that the remedy sought here fits all

too comfortably within this Court’s “functional approach” for evaluating whether something is properly

considered a tax. NFIB v. Sebelius, 567 U.S. 519, 565

(2012).

As an initial matter, it does not matter whether litigants label their scheme a “tax” or not, as the Court

looks to its “practical operation.” Id. at 564–65 (noting

the “label” is not determinative and concluding something labeled a “penalty” was in reality a tax); accord

Nelson v. Sears, Roebuck & Co., 312 U.S. 359, 363

(1941) (“In passing on the constitutionality of a [State]

tax law ‘we are concerned only with its practical operation, not its definition or the precise form of descriptive words which may be applied to it.’”) (citation

omitted).

And, as explained above, the remedy sought in

these nuisance suits “looks like a tax in many respects.” NFIB, 567 U.S. at 563. For Boulder City and

County, the nuisance litigation “yields the essential

feature of any tax: It produces at least some revenue

for the Government.” Id. Indeed, the revenue to Boulder County and other state and local governments

from these nuisance suits would far exceed the $4

10

billion per year at issue in NFIB. And the tax-collecting body, by bringing the lawsuit, makes itself the enforcer of the tax, just like the IRS was the enforcer in

NFIB. Id. at 566 (finding relevant whether the body

responsible for “collecting revenue” enforced the alleged tax).

The nuisance litigation fits this Court’s framework

for a tax in other ways, too. It is a paradigmatic example of a scheme that “will raise considerable revenue” and is “intended to affect individual conduct,”

which is a type of tax this Court has recognized is

“nothing new.” Id. at 567. This Court is familiar with

many “obviously regulatory measures” that are in fact

taxes aimed at curtailing conduct, such as the high

taxes placed on cigarettes, marijuana, and sawed-off

shotguns. Id. The nuisance litigation is no different,

as it seeks to impose a de facto carbon tax as a means

of curtailing the production of fossil fuels. This, on its

face, “leaves an individual with a lawful choice to do

or not do a certain act, so long as he is willing to pay

a tax levied on that choice.” Id. at 574. But for fossil

fuel producers, that choice is illusory, as the nuisance

litigation, if permitted to continue, leaves energy producers with the choice of ceasing operations or paying

such an extensive series of taxes across the country

that they will be forced to “declar[e] bankruptcy.”

Comments of David Bookbinder, supra.

II.

Boulder’s De Facto Carbon Tax Is

Unlawful on Multiple Grounds

Viewed through the lens of the Court’s cases concerning state taxation and regulation, Boulder’s lawsuit and the remedy it seeks contravene many constitutional doctrines. Among them are the federalism

11

and separation-of-powers doctrines raised by Petitioners. Here, The Buckeye Institute focuses on the

remedy’s conflict with principles limiting extraterritorial taxation under the Commerce Clause and Due

Process Clause and its intrusion on foreign affairs

powers reserved to the federal government.

A. This Lawsuit Seeks to Impose an

Unconstitutional Extraterritorial Tax

“The Due Process and Commerce Clauses forbid

the States to tax ‘extraterritorial values.’” MeadWestvaco Corp. ex rel. Mead Corp. v. Ill. Dep’t of Revenue,

553 U.S. 16, 19 (2008) (quoting Container Corp. of

Am. v. Franchise Tax Bd., 463 U.S. 159, 164 (1983)).

“It is now established beyond dispute that the Commerce Clause was not merely an authorization to Congress to enact laws for the protection and encouragement of commerce among the States, but by its own

force created an area of trade free from interference

by the States. … the Commerce Clause even without

implementing legislation by Congress is a limitation

upon the power of the States.” Bos. Stock Exch. v.

State Tax Comm’n, 429 U.S. 318, 328 (1977) (cleaned

up).

“State sovereign authority is bounded by the

States’ respective borders.” Fuld v. Palestine Liberation Org., 145 S. Ct. 2090, 2104 (2025). Pursuant to

that baseline, the Commerce Clause “precludes the

application of a state statute to commerce that takes

place wholly outside of the State's borders, whether or

not the commerce has effects within the State,” Healy

v. Beer Inst., Inc., 491 U.S. 324, 336 (1989) (citation

and quotation marks omitted). This is the notion

12

embedded in the bedrock of the federalist “Constitution’s structure,” Nat’l Pork Producers Council v.

Ross, 598 U.S. 356, 376 (2023), that a State is “without power to exercise ‘extra territorial jurisdiction,’

that is, to regulate and control activities wholly beyond its boundaries[,]” Watson v. Emp’s Liability Assurance Corp., 348 U.S. 66, 70 (1954).

The Commerce Clause applies to state taxes where,

as here, the tax reaches interstate conduct. For this

Court to uphold such a tax, it must satisfy at least

four elements: the tax is legal only when it “(1) applies

to an activity with a substantial nexus with the taxing

State, (2) is fairly apportioned, (3) does not discriminate against interstate commerce, and (4) is fairly related to the services the State provides.” Barclays

Bank PLC v. Franchise Tax Bd. of California, 512

U.S. 298, 310–11 (1994) (citing Complete Auto

Transit, Inc. v. Brady, 430 U.S. 274, 279 (1977)). Similarly, the Due Process clause requires that state

taxes (1) have “some definite link, some minimum

connection, between a state and the person, property

or transaction it seeks to tax” and (2) “must be rationally related to ‘values connected with the taxing

State.’” N. Carolina Dep’t of Revenue v. The Kimberley

Rice Kaestner 1992 Fam. Tr., 588 U.S. 262, 269 (2019)

(citations omitted). Under Due Process, a state may

only “tax an apportioned sum of the corporation’s multistate business.” Allied-Signal, Inc. v. Dir., Div. of

Tax’n, 504 U.S. 768, 773 (1992).

This first prong for the Commerce Clause is “closely

related…to the due process requirement that there be

‘some definite link, some minimum connection,

13

between a state and the person, property or transaction it seeks to tax.’” S. Dakota v. Wayfair, 585 U.S.

162, 177 (2018) (quoting Miller Brothers Co. v. Maryland, 347 U.S. 340, 344–45 (1954)) (internal citation

omitted). It “asks whether the tax applies to an activity with a substantial nexus with the taxing State”

and whether the taxpayer “avails itself of the substantial privilege of carrying on business in that jurisdiction.” Id. at 188.

Indeed, that requirement undergirds “both the Due

Process and Commerce Clauses” and necessitates

that “a State may not tax value earned outside its borders.” Allied-Signal, 504 U.S. at 777 (citing Miller

Brothers Co., 347 U.S. at 344–45). And the inquiry

“whether the taxing power exerted by the state bears

fiscal relation to protection, opportunities and benefits given by the state” is “subsumed in both constitutional requirements.” MeadWestvaco Corp., 553 U.S.

at 24–25.

In short, Colorado may only tax what may “in fairness be attributed to the taxpayer’s activities within

the State.” Allied-Signal, 504 U.S. at 780. This is true

for multinational companies like Petitioners. See id.

For example, in South Dakota v. Wayfair, the Court

found the nexus “sufficient” because South Dakota’s

tax was tailored and applied “only to sellers that deliver more than $100,000 of goods or services into

South Dakota or engage in 200 or more separate

transactions for the delivery of goods and services into

the State on an annual basis. … This quantity of business could not have occurred unless the seller availed

14

itself of the substantial privilege of carrying on business in South Dakota.” Wayfair, 585 U.S. at 188.

But there is no “limiting principle,” Allied-Signal,

504 U.S. at 780, to the relief that Boulder City and

County seek in this lawsuit. They seek to impose a

one-time tax on all of Petitioners’ ongoing conduct all

over the entire world, without apportionment limited

to conduct linked to Colorado. It is not taxing conduct

based on benefits or protection Colorado gives to Petitioners. Rather, the damages award is meant to be a

tax award for all of the emissions Petitioners allegedly contribute to around the world. As Petitioners

note, “plaintiffs allege harms … from the effects of increased greenhouse-gas emissions on the global climate.” Pet. Br.37. A one-time corporate tax on such

ongoing global conduct has no nexus to Colorado’s

“protections” or “benefits” for Petitioners. There is no

“rational relationship between” the damages sought

“and the intrastate values of the enterprise.”

ASARCO Inc. v. Idaho State Tax Comm’n, 458 U.S.

307, 328 (1982). Accordingly, were the remedy considered a tax, it would be unconstitutional, and the same

sovereignty- and federalism-based principles underlying the Court’s tax-related cases equally bar extraterritorial regulation through the litigation of state-law

claims.

B. Boulder’s Carbon Tax Interferes with

Federal Constitutional Prerogatives

to Set Foreign Policy

The Constitution’s Foreign Commerce and Foreign

Affairs Clauses each prohibit a State, through

15

taxation, from tramping on the constitutional prerogatives of the federal branches. Here, Boulder’s de facto

carbon tax violates both Clauses.

1. First, this Court’s higher standards for a state

tax that affects foreign commerce dooms Colorado’s

lawsuit. “In the unique context of foreign commerce,

a State’s power is further constrained because of the

special need for federal uniformity.” Barclays Bank

PLC, 512 U.S. at 311 (cleaned up). “A tax affecting

foreign commerce therefore raises two concerns in addition to the four delineated in Complete Auto.” Id.

“The first is prompted by the enhanced risk of multiple taxation. The second relates to the Federal Government’s capacity to speak with one voice when regulating commercial relations with foreign governments.” Id. (cleaned up).

The lawsuit interferes with the federal government’s ability to speak with one voice on global carbon

taxes, emissions, and foreign policy regarding the

same. “[A] state tax at variance with federal policy

will violate the ‘one voice’ standard if it either implicates foreign policy issues which must be left to the

Federal Government or violates a clear federal directive.” Container Corp., 463 U.S. at 194. Here, the

Boulder lawsuit violates both options.

Global carbon taxes must be left to the federal government. In 1992, President George H. W. Bush

signed, and the Senate unanimously ratified, the

United Nations Framework Convention on Climate

Change, May 9, 1992, S. Treaty Doc. No. 102-38, 1771

U.N.T.S. 107 (entered into force Mar. 21, 1994), the

16

“ultimate objective” of which was the “stabilization of

greenhouse gas concentrations in the atmosphere at a

level that would prevent dangerous anthropogenic interference with the climate system.” Id., Art. 2. 39.

Under the Framework Convention, “[a]ll Parties,” including the United States, “shall . . . . (b) [f]ormulate,

implement, publish and regularly update national

and, where appropriate, regional programmes containing measures to mitigate climate change by addressing anthropogenic emissions by sources and removals by sinks of all greenhouse gases not controlled

by the Montreal Protocol, and measures to facilitate

adequate adaptation to climate change [and] (c)[p]romote and cooperate in the development, application

and diffusion, including transfer, of technologies,

practices and processes that control, reduce or prevent anthropogenic emissions of greenhouse gases not

controlled by the Montreal Protocol in all relevant sectors . . . .” Id., Art. 4.1(b), (c). Congress has tasked the

State Department “to formulate United States foreign

policy with reference to environmental matters relating to climate.” Massachusetts v. EPA, 549 U.S. 497,

534 (2007).

In that vein, the President issued Executive Order

14260 on April 8, 2025, outlining his policy that the

Attorney General should look at “State laws purporting to address ‘climate change’ … and funds to collect

carbon penalties or carbon taxes.” 8 Similarly, the

8

Available at https://www.whitehouse.gov/presidential-actions/2025/04/protecting-american-energy-from-state-overreach/.

17

Administration has refused to join in a proposed

global carbon tax stating:

President Trump has made it clear that

the United States will not accept any international environmental agreement

that unduly or unfairly burdens the

United States or harms the interests of

the American people. Next week, members of the IMO will vote on the adoption

of a so-called NZF aimed at reducing

global carbon dioxide gas emissions from

the international shipping sector. This

will be the first time that a UN organization levies a global carbon tax on the

world.

The Administration unequivocally rejects this proposal before the IMO and

will not tolerate any action that increases costs for our citizens, energy providers, shipping companies and their

customers, or tourists. 9

Similarly, the Administration has brought two lawsuits in New York and Vermont 10 under the theory

9 Joint Statement by Secretary of State Rubio, Secretary of En-

ergy Wright, and Secretary of Transportation Duffy (Oct. 10,

2025), available at https://www.state.gov/releases/office-of-thespokesperson/2025/10/taking-action-to-defend-america-fromthe-uns-first-global-carbon-tax-the-international-maritime-organizations-imo-net-zero-framework-nzf.

10 United States v. New York, No. 1:25-cv-03656 (S.D.N.Y.);

United States v. Vermont, No. 2:25-cv-00463 (D. Vt.).

18

that the States are interfering with the Administration’s prerogative to set global emissions policies.

Accordingly, these issues should be left to the federal government.

Second, the lawsuit violates a clear federal directive—the Clean Air Act. “The [Clean Water] Act

pre-empts state law to the extent that the state law is

applied to an out-of-state point source.” Int’l Paper Co.

v. Ouellette, 479 U.S. 481, 500 (1987). The Clean Air

Act’s comprehensive framework, which includes specific provisions for regulating emissions, 42 U.S.C.

§§ 7410, 7411, 7521, preempts state laws that attempt to regulate out-of-state. Thus “the only state

suits that remain available” to provide redress for injuries allegedly caused by interstate emissions are

“those specifically preserved by” the Clean Air Act.

Ouellette, 479 U.S. at 500. Those are quite limited. See

id.; cf. 42 U.S.C. § 7416. The federal directive is unmistakable: To the extent States may regulate emission—through lawsuits or elsewise—that regulation

must be source-State and constitutional. For all the

reasons discussed herein and by Petitioners, this lawsuit is constrained to neither the bounds of Colorado

nor the bounds of the Constitution.

2. Boulder’s de facto global carbon tax also would

deny the federal political branches their constitutional prerogatives to set foreign policy.

Specifically, it conflicts with the current Administration’s express policies on carbon taxes, thereby

triggering what been dubbed “dormant foreign affairs

preemption.” Am. Ins. Ass’n v. Garamendi, 539 U.S.

19

396, 439 (2003) (Ginsburg, J., dissenting). This genre

of preemption sprung from Zschernig v. Miller, where

this Court determined an Oregon probate statute prohibiting inheritance by a nonresident alien where the

foreign heir might face confiscation in the foreign

country was invalid as an “intrusion by the State into

the field of foreign affairs which the Constitution entrusts to the President and the Congress.” 389 U.S.

429, 432 (1968).

“Preemption based on constitutional structure is

especially important when state law intrudes upon

the Federal Government’s exclusive authority to conduct relations with other nations.” Hencely v. Fluor

Corp., 608 U.S. __, __, 146 S. Ct. 1086, 1103 (2026)

(Alito, J., dissenting). It is only the “Federal Government” that “is entrusted with full and exclusive responsibility for the conduct of affairs with foreign sovereignties.” Hines v. Davidowitz, 312 U.S. 52, 63

(1941). Our constitutional system therefore “imperatively requires that federal power in the field affecting

foreign relations be left entirely free from local interference.” Id.; cf. United States v. Belmont, 301 U.S.

324, 331 (1937) (“complete power over international

affairs is in the national government and is not and

cannot be subject to any curtailment or interference

on the part of the several states”).

Although there is a reserved “power of the States to

tax for the support of their own governments,” Gibbons v. Ogden, 9 Wheat. 1, 199, 6 L.Ed. 23 (1824), such

power is “limit[ed]” by the Constitution, Bos. Stock

Exch., 429 U.S. at 328–29, including by foreign affairs

preemption.

20

This Court has suggested that where “a State has

acted within what Justice Harlan called its ‘traditional competence,’ but in a way that affects foreign

relations,” the Court would look at the “the strength

of the state interest, judged by standards of traditional practice, when deciding how serious a conflict

must be shown before declaring the state law

preempted.” Garamendi, 539 U.S. at 420 & n.11. The

Court left open the possibility of also weighing “the

strength of the federal foreign policy interest.” Id. Regardless, the end point is straightforward: “the likelihood that state legislation will produce something

more than incidental effect in conflict with express

foreign policy of the National Government would require preemption of the state law.” Id.

Here, Boulder’s attempt to impose a global carbon

tax traipses over the Administration’s policies on

those taxes, including ongoing multilateral talks. As

described above, the federal government seeks to

speak with one voice on environmental issues. The result is clear: It is the Administration’s prerogative to

set foreign policy on the environment, including

global carbon taxes, and it has done so by disapproving of state carbon taxes and disapproving of proposed

global carbon taxes. Accordingly, under the Garamendi interest-balancing test, this is (1) a foreign affairs issue trusted to the political branches; (2) delegated to the President; and (3) explicitly expressed by

the President. The strength of the federal interest is

evinced in the consistent conduct of the political

branches to retain the power to regulate environmental issues.

21

Lawsuits like this one are functionally equivalent

to the imposition of a corporate tax, as explained

above. Boulder’s extremely costly approach substantially involves the global economy, a dynamic that

could be repeated by many other states using tort litigation as a de facto carbon tax. Yet this allows states

to, under another name, issue the exact types of global

carbon taxes the President has put under scrutiny as

interfering with the political branches’ environmental

policymaking. There is more than a “likelihood that

state legislation will produce something more than incidental effect in conflict with express foreign policy

of the National Government,” so this “would require

preemption of the state [lawsuits].” Garamendi, 539

U.S. at 420.

Nor do the governments here have a strong interest

in a de facto global carbon tax, as judged by standards

of traditional practice. Although corporate taxation is

a traditional practice of states, regulation of out-ofstate conduct, especially with global environmental

stakes, cannot be said to be “traditional” state regulation in any sense. Boulder does not have the legal

right to impose a global carbon tax against the federal

political branches’ will. This lawsuit should fail.

22

CONCLUSION

The decision below should be reversed.

Respectfully submitted,

ROBERT ALT

THE BUCKEYE

INSTITUTE

88 East Broad Street,

Suite 1300

Columbus, OH 43215

(614) 224-4422

robert@buckeyeinstitute.org

ANDREW M. GROSSMAN

Counsel of Record

BENJAMIN D. JANACEK

CALEB ACKER

BAKER & HOSTETLER LLP

1050 Connecticut Ave., N.W.

Washington, D.C. 20036

(202) 861-1697

agrossman@bakerlaw.com

Counsel for the Amicus Curiae

MAY 21, 2026