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, INC., ET AL.,

v.

Petitioners,

COUNTY COMMISSIONERS OF BOULDER COUNTY, ET AL.,

Respondents.

On Writ of Certiorari to the

Colorado Supreme Court

BRIEF OF AMICUS CURIAE

CONSUMERS’ RESEARCH

IN SUPPORT OF PETITIONERS

Tyler R. Green

Counsel of Record

CONSOVOY MCCARTHY PLLC

222 S. Main St., 5th Fl.

Salt Lake City, UT 84101

(703) 243-9423

tyler@consovoymccarthy.com

Cody Ray Milner

CONSOVOY MCCARTHY PLLC

1600 Wilson Blvd., Ste. 700

Arlington, VA 22209

Counsel for Amicus Curiae

i

QUESTION PRESENTED

(1) Whether federal law precludes state-law claims

seeking relief for injuries allegedly caused by the

effects of interstate and international greenhouse-gas

emissions on the global climate; and

(2) Whether this Court has statutory and Article III

jurisdiction to hear this case.

ii

TABLE OF CONTENTS

Question Presented ......................................................i

Table of Contents ....................................................... ii

Table of Authorities ................................................... iii

Interest of Amicus Curiae ........................................... 1

Summary of Argument................................................ 2

Argument ..................................................................... 3

I. States Have Significant Authority—But Only

Within Their Own Borders .................................... 3

A. The doctrine that States can regulate only

within their territorial jurisdiction derives

from the law of nations and predates the

Founding ........................................................... 5

B. This Court has consistently applied the

principle of territorial jurisdiction to prevent

a State from regulating conduct in other

States .............................................................. 16

C. This Court’s precedent on interstate

environmental disputes confirms that no

single State may govern conduct beyond its

borders ............................................................ 21

II. Boulder County’s Lawsuit Violates the Doctrine

of Territorial Jurisdiction .................................... 29

Conclusion ................................................................. 32

iii

TABLE OF AUTHORITIES

Cases

Alden v. Maine,

527 U.S. 706 (1999) ........................................... 3, 5

Am. Electric Power Co. v. Connecticut (“AEP”),

564 U.S. 410 (2011) ............................................. 28

Baldwin v. G.A.F. Seelig, Inc.,

294 U.S. 511 (1935) ........................... 13, 16, 17, 30

Banco Nacional de Cuba v. Sabbatino,

376 U.S. 398 (1964) ............................................. 26

BMW of N. Am., Inc. v. Gore,

517 U.S. 559 (1996) ....................... 4, 15, 20, 30, 31

Bonaparte v. Tax Court,

104 U.S. 592 (1881) ................................. 18, 19, 29

Burnet v. Brooks,

288 U.S. 378 (1933) ............................................. 17

Camps Newfound/Owatonna, Inc., v. Town of

Harrison, 520 U.S. 564 (1997) ............................ 12

City of Milwaukee v. Illinois (“Milwaukee II”),

451 U.S. 304 (1981) ............................................. 26

City of New York v. Chevron Corp.,

993 F.3d 81 (2d Cir. 2021) ...................... 22, 27, 29

Cole v. Cunningham,

133 U.S. 107 (1890) ............................................. 15

Connecticut v. Massachusetts,

282 U.S. 660 (1931) ............................................. 24

Edgar v. MITE Corp.,

457 U.S. 624 (1982) ....................................... 13, 19

iv

Energy & Env’t Legal Inst. v. Epel,

793 F.3d 1169 (10th Cir. 2015) ........................... 16

Franchise Tax Bd. of Cal. v. Hyatt,

587 U.S. 230 (2019) ..................................... 3, 5, 17

Fuld v. Palestine Liberation Org.,

606 U.S. 1 (2025) ................................... 4, 6, 17, 30

Georgia v. Tennessee Copper Co.,

206 U.S. 230 (1907) ....................................... 23, 24

Hanson v. Denckla,

357 U.S. 235 (1958) ............................................. 18

Healy v. Beer Institute, Inc.,

491 U.S. 324 (1989) ........................... 13, 15, 17, 20

Hinderlider v. La Plata River & Cherry Creek Ditch

Co., 304 U.S. 92 (1938) ................................. 24, 25

Hughes v. Fetter,

341 U.S. 609 (1951) ............................................. 10

Huntington v. Attrill,

146 U.S. 657 (1892) ............................................. 18

Illinois v. City of Milwaukee (“Milwaukee I”),

406 U.S. 91 (1972) ......................................... 25, 26

Illinois v. City of Milwaukee (“Milwaukee III”),

731 F.2d 403 (7th Cir. 1984) ............................... 27

Int’l Paper Co. v. Ouellette,

479 U.S. 481 (1987) ....................................... 28, 29

Iowa v. Illinois,

147 U.S. 1 (1893) ................................................. 24

Kansas v. Colorado,

206 U.S. 46 (1907) ................. 10, 18, 22, 23, 30, 31

v

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

565 U.S. 625 (2012) ............................................. 20

Livermore v. Jenckes,

62 U.S. (21 How.) 126 (1858) .............................. 16

Mallory v. Norfolk S. Ry. Co.,

600 U.S. 122 (2023) ....................................... 18, 19

Minnesota v. Am. Petroleum Inst.,

63 F.4th 703 (8th Cir. 2023) ............................... 22

Missouri v. Illinois,

200 U.S. 496 (1906) ....................................... 22, 23

N.Y. Life Ins. Co. v. Head,

234 U.S. 149 (1914) ................................. 16, 18, 19

Nat’l Pork Producers Council v. Ross,

598 U.S. 356 (2023) ......................... 4, 9, 12, 13, 17

New Jersey v. New York,

283 U.S. 336 (1931) ............................................. 24

North Carolina ex rel. Cooper v. TVA,

615 F.3d 291 (4th Cir. 2010) ............................... 29

Ogden v. Saunders,

25 U.S. (12 Wheat.) 213 (1827)..................... 17, 18

Paul v. Virginia,

75 U.S. (8 Wall.) 168 (1868) ................................ 11

Phillips Petroleum Co. v. Shutts,

472 U.S. 797 (1985) ............................................. 14

Pollard v. Hagan,

44 U.S. 212 (1845) ................................................. 5

PPL Mont., LLC v. Montana,

565 U.S. 576 (2012) ............................................... 5

vi

Shaffer v. Heitner,

433 U.S. 186 (1977) ............................................. 17

Shelby County v. Holder,

570 U.S. 529 (2013) ........................................... 3, 5

State Farm Mut. Auto. Ins. Co. v. Campbell,

538 U.S. 408 (2003) ................................... 3, 15, 30

Strader v. Graham,

51 U.S. (10 How.) 82 (1850) ................................ 18

Toomer v. Witsell,

334 U.S. 385 (1948) ............................................. 11

Woodruff v. Parham,

75 U.S. (8 Wall.) 123 (1869) ................................ 12

World-Wide Volkswagen v. Woodson,

444 U.S. 286 (1980) ............................................. 14

Constitutional Provisions

U.S. Const. art. I, §10 ................................................ 11

U.S. Const. art. IV, §1 ................................................. 9

U.S. Const. art. IV, §2 ............................................... 11

U.S. Const. amend. XIV ............................................ 14

Other Authorities

Vattel, The Law of Nations (J. Chitty ed. 1854) .... 6, 9

Kent, Commentaries on American Law (New York,

O. Halsted, 1827) .................................................. 9

Laycock, Equal Citizens of Equal and Territorial

States, 92 Colum. L. Rev. 249 (1992) ................. 10

Regan, Siamese Essays, 85 Mich. L. Rev. 1865

(1987) ................................................... 9, 12, 17, 19

vii

Rosen, State Extraterritorial Powers Reconsidered,

85 Notre Dame L. Rev. 1133 (2010) ............. 10, 14

Shearer, Locating Extraterritoriality, 100 Bost. U.

L. Rev. 1501 (2020) ............................................... 7

Story, Commentary on the Conflict of Laws (1834).... 8

The Debates in the Several State Conventions on

the Adoption of the Federal Constitution

(Jonathan Elliot ed., 2d ed. 1836) ................ 6, 7, 8

The Federalist, No. 45 (James Madison) (Clinton

Rossiter ed., 1961) ................................................. 5

1

INTEREST OF AMICUS CURIAE

Consumers’ Research is an independent

educational 501(c)(3) nonprofit organization whose

mission is to increase the knowledge and

understanding of issues, policies, products, and

services of concern to consumers and to promote the

freedom to act on that knowledge and understanding.

Consumers’ Research believes that the cost, quality,

availability, and variety of goods and services used or

desired by American consumers—from both the

private and public sectors—are improved by greater

consumer knowledge and freedom. To that end,

Consumers’ Research engages in research, policy

advocacy, and public engagement initiatives.

Consumers’ Research has extensive experience

studying consumer-related issues involving efforts to

use litigation and regulatory pressure to reshape the

national energy market in ways that drive up costs

and reduce choice for consumers across the country.

The holding of the Colorado Supreme Court, if left in

place, would expose energy producers to a patchwork

of inconsistent state-court judgments and effectively

allow Colorado—or any other State—to dictate energy

policy for the entire Nation. That would reduce

competition, raise prices, and diminish the energy

options available to American consumers in every

State. For these reasons, Consumers’ Research has a

significant interest in this case. *

Under Rule 37.6, no counsel for a party authored this brief in

whole or in part, and no person other than amicus curiae, its

members, or its counsel made a monetary contribution to its

preparation or submission.

*

2

SUMMARY OF ARGUMENT

In our federal system, one State cannot govern the

whole Nation. Yet the Colorado Supreme Court’s

judgment blesses Boulder County’s efforts to do

precisely that here. Invoking state nuisance law,

Boulder County has obtained a judicial decree that

regulates conduct occurring outside of Colorado’s

borders—in States where that conduct was both

lawful and beyond Colorado’s sovereign authority.

Federal law may preempt Boulder County’s

gambit. See Pet. Br. 12-14. But other federalism

concerns presented here—and by similar gambits

throughout the country—warrant a different result.

Preemption assumes that absent the federal law, a

State would have authority to regulate. Yet Colorado

has never had authority to extend its laws beyond its

borders and regulate conduct occurring in other

sovereign States. That principle of territorial

jurisdiction prohibits a State’s laws from applying

outside its borders. And that principle applies with

full force to state common-law judgments. After all, a

State exercises sovereign power not only through

statutes and regulations, but also through applying

its common law in civil litigation. Damages,

abatement, and remediation orders are powerful tools

for governing conduct, and States cannot use those

litigation tools to accomplish what direct legislation

could not.

This dispute implicates more than mere energy

policy. If Colorado may impose its nuisance law on

lawful conduct occurring in other States, every State

may try to use its own tort law to regulate every

3

nationally significant industry. The resulting

patchwork of competing state-law commands would

wreak havoc on consumers; nationwide commerce

would be governed by the most aggressive State’s

preferred policy. The Constitution does not permit

that result. Because Boulder County’s claims violate

the doctrine of territorial jurisdiction, the judgment

below should be reversed.

ARGUMENT

I. States Have Significant Authority—But Only

Within Their Own Borders.

When the Founders ratified the Constitution, the

longstanding “historic tradition” drawn from the law

of nations was that “all the States enjoy equal

sovereignty.” Shelby County v. Holder, 570 U.S. 529,

540 (2013) (cleaned up). Ratifying the Constitution

both “preserve[d] the sovereign status of the States,”

Alden v. Maine, 527 U.S. 706, 714 (1999), and

“transform[ed]” the States “from a loose league of

friendship into a perpetual Union based on the

‘fundamental principle of equal sovereignty among

the States,’” Franchise Tax Bd. of Cal. v. Hyatt, 587

U.S. 230, 246 (2019) (cleaned up). At the core of that

inherent sovereignty lies the power of each State to

prescribe rules governing conduct within its own

territory. After all, “[a] basic principle of federalism is

that each State may make its own reasoned judgment

about what conduct is permitted or prescribed within

its borders.” State Farm Mut. Auto. Ins. Co. v.

Campbell, 538 U.S. 408, 422 (2003).

4

But coequal sovereignty among States has a

necessary corollary: Each State’s power within its own

borders stops at those borders. This Court reiterated

just last Term that a “state[’s] sovereign authority is

bounded by the States’ respective borders.” Fuld v.

Palestine Liberation Org., 606 U.S. 1, 14 (2025). Each

State’s residual sovereignty under the Constitution

carries with it an inherent constraint on its

prescriptive power. A State may not prescribe rules

that directly govern conduct beyond its “territorial

limitations.” Id. (cleaned up); see also, e.g., Nat’l Pork

Producers Council v. Ross, 598 U.S. 356, 376 n.1

(2023) (discussing “territorial limits of state authority

under the Constitution’s horizontal separation of

powers”); BMW of N. Am., Inc. v. Gore, 517 U.S. 559,

572 (1996) (invoking the “principles of state

sovereignty and comity”).

This general principle—that a State cannot

regulate conduct occurring outside its territorial

jurisdiction—stems from the preexisting inherent

sovereignty of States. It’s embodied in provisions of

the Constitution that address extraterritorial

restrictions on States. And this Court has employed it

to bar individual States from directly imposing their

will on other States by regulating conduct outside

their territorial jurisdiction. This principle of

territorial jurisdiction functions as a doctrine of

constitutional law and prevents Colorado from using

its tort law to regulate fossil fuel activities that are

outside Colorado’s territorial jurisdiction and that are

lawful where they occur.

5

A. The doctrine that States can regulate only

within their territorial jurisdiction

derives from the law of nations and

predates the Founding.

1. Upon declaring independence, the Colonies laid

claim “to all the rights and powers of sovereign

states.” Franchise Tax Bd., 587 U.S. at 237-38. When

those then-States later came together to form a union,

they enshrined a constitutional order that “preserves

the sovereign status of the States,” Alden, 527 U.S. at

714, and reserves to each State “numerous and

indefinite” sovereign powers, The Federalist, No. 45,

at 289 (James Madison) (Clinton Rossiter ed., 1961).

Each State retained authority over “all the objects

which, in the ordinary course of affairs, concern the

lives, liberties, and properties of the people, and the

internal order, improvement, and prosperity of the

State.” Id. And against one another, the States stand

“upon an equal footing, in all respects whatever.”

Pollard v. Hagan, 44 U.S. 212, 224 (1845). Thus, the

Founding proceeded from the “historic tradition that

all the States enjoy equal sovereignty,” Shelby County,

570 U.S. at 540, and that “[t]he States in the Union

are coequal sovereigns under the Constitution,” PPL

Mont., LLC v. Montana, 565 U.S. 576, 591 (2012).

This principle of equal sovereignty among States

derives from the law of nations that preexisted the

constitutional order itself. Swiss jurist Emmerich de

Vattel wrote in his 1758 Law of Nations that each

sovereign state has exclusive authority within its own

territory, and no sovereign state could rule over or

judge what occurs in another sovereign state. A

“sovereign ... alone is directly interested in the

6

manner in which” it “makes use of [its] power,” so no

“foreign power” can second-guess “the administration

of that sovereign,” or “set himself up for a judge of his

conduct, and to oblige him to alter it.” 2 Vattel, The

Law of Nations §54, p. 155 (J. Chitty ed. 1854).

Vattel “was ‘widely consulted by the constitutional

generation in the United States,’ and was ‘invariably

invoked as authoritative on matters of international

law.’” Fuld, 606 U.S. at 28 n.1 (Thomas, J., concurring

in judgment). His view of the law of nations and

States’ inherent, overlapping sovereignty found its

way into our constitutional ratification debates. Those

discussions of each State’s sovereignty confirm that

the Framers understood territorial jurisdiction as a

structural limit on State authority, such that States

are sovereign within their own borders and may not

regulate conduct that occurs outside their borders and

is lawful in other States where it occurs.

At the Massachusetts Convention, William Heath

articulated the baseline principle. “Each state is

sovereign and independent to a certain degree, and

the states have a right, and they will regulate their

own internal affairs as to themselves appears proper.”

2 The Debates in the Several State Conventions on the

Adoption of the Federal Constitution 115 (Jonathan

Elliot ed., 2d ed. 1836) (emphasis added). Heath was

equally explicit about that principle’s corollary—

Massachusetts had no power to interfere with slavery

in the southern states, and “no right to compel” the

“Southern States” to conform to Massachusetts’ own

anti-slavery laws. Id. (emphasis added). Heath

acknowledged that joining the Union neither

expanded nor restricted the inherent law of nations

7

afforded to

Massachusetts’ internal

affairs.

Massachusetts’ sovereignty still could not be

encroached upon (except in the areas ceded to the

federal government), and it still could not encroach on

any other sovereign State. See id.; see also Shearer,

Locating Extraterritoriality, 100 Bost. U. L. Rev. 1501,

1527 (2020).

James Madison confirmed the same principle from

the opposite direction at the Virginia Convention.

Madison acknowledged that an enslaved person who

reached a free state “becomes emancipated by their

laws,” thus conceding that Virginia’s slavery laws had

no force beyond Virginia’s borders. 3 Debates, supra,

453. The laws of the states, Madison stated, were

“uncharitable to one another in this respect.” Id. But

Madison acknowledged that the laws of nations meant

that “Virginia could not project its laws beyond its

borders absent some constitutional authorization to

the contrary.” Shearer, supra, 1528.

Other

delegates

underscored

the

same

understanding of the territorial-jurisdiction principle.

In New York, James Duane noted that “it will be in

the power of every state” to regulate for themselves

the matters left for the States, and asked rhetorically

whether “[i]s every state to be compelled to adopt our

ideas on all subjects?” and “[w]ill it not seem

extraordinary that any one state should presume to

dictate to the Union?” 2 Debates, supra, 327-28. In

the same debate, Melacton Smith emphasized that

state governments were designed for “local purposes”

and could not operate beyond that sphere. Id. at 332.

And in Pennsylvania, James Wilson grounded the

entire system in popular sovereignty—sovereign

8

States could exercise power only to the extent it was

granted by its people. Id. at 443-44. A State therefore

cannot regulate those who never submitted to its

authority, because the people could not have conferred

such power in the first place.

Together, these statements demonstrate that the

Framers viewed territorial jurisdiction as a

preexisting aspect of sovereignty inherent in

statehood that would survive the federal compact. A

sovereign that could project its laws into sister states

would undermine the coequality on which the Union

was premised. The Constitution did not create that

limit—it codified and enforced one that the Framers

universally acknowledged already existed.

Given its ubiquity, the same principle moved from

the ratification debates into the foundational legal

treatises of the early Republic. The doctrine of

territorial jurisdiction found its way into Justice

Joseph Story’s seminal treatise on conflicts of laws.

According to Justice Story, every sovereign State

“establishes the exclusive jurisdiction ... within its

own territor[y].” Story, Commentary on the Conflict of

Laws §8 (1834). This meant that the laws of a State

“can have no intrinsic force, proprio vigore, except

within the territorial limits and jurisdiction” of that

State, and “no state or nation can, by its laws, directly

affect, or bind property out of its own territory.” Id.

§§7, 20. Likewise, “[n]o nation can be justly required

to yield up its own fundamental policy and

institutions in favour of those of another nation.’”

Id. §25.

9

Others shared Story’s understanding. His

contemporary, Chancellor James Kent, stated the

anti-extraterritorial legislation principles with equal

clarity in his Commentaries on American Law: “[I]f a

statute ... was to have the same effect in one state as

in another, then one state would be dictating laws for

another, and a fearful collision of jurisdiction would

instantly follow.” 2 Kent, Commentaries on American

Law 100 (New York, O. Halsted, 1827). For Kent, the

principle followed from the nature of sovereignty

itself, since “each nation has a right to govern itself as

it deems proper, and no one nation is entitled to

dictate” the “course of internal policy, to another.” Id.

at 91 (citing Vattel).

2. From the preexisting law of nations, early

treatises, and ratification debates, the general

principle that a State cannot impose its will outside of

its territorial boundaries found its way into the

Constitution itself. The doctrine of territorial

jurisdiction is “one of those foundational principles of

our federalism which we infer from the structure of

the Constitution as a whole.” Regan, Siamese Essays,

85 Mich. L. Rev. 1865, 1885 (1987). The principle that

States must respect the sovereignty of sister States

and may not regulate conduct occurring beyond their

own borders appears in several constitutional

guarantees. Cf. Nat’l Pork Producers, 598 U.S. at 40809 (Kavanaugh, J., concurring).

First, the Full Faith and Credit Clause commands

that “Full Faith and Credit shall be given in each

State to the public Acts, Records, and judicial

Proceedings of every other State.” U.S. Const. art. IV,

§1. At its core, that rule requires mutual respect

10

among coequal sovereigns. The Clause forbids any

State from “adopting any policy of hostility to the

public Acts” of another State. Carroll v. Lanza, 349

U.S. 408, 413 (1955). And it imposes a “constitutional

obligation to enforce the rights and duties validly

created under the laws of other states.” Hughes v.

Fetter, 341 U.S. 609, 611 (1951).

The Full Faith and Credit Clause has an obvious

territorial-jurisdiction dimension. Consider the

context here: When a State applies its own tort law to

impose liability for emissions occurring entirely in

another State, it does more than adjudicate a

dispute—it also displaces the source State’s policy

judgments about how emissions should be regulated.

The source State’s judgments—reflected in its

statutes, permits, or regulatory schemes—are “public

Acts” entitled to respect under Article IV. A contrary

approach would allow one State, through its tort law,

to override another’s sovereign decisions governing

conduct within its own territory. That is precisely the

“hostility” the Clause forbids. See Kansas v. Colorado,

206 U.S. 46, 95-97 (1907) (no state “can impose its own

legislation” or “enforce its own policy upon the

other[s]”). And it helps to explain why “the Full Faith

and Credit Clause is the more natural source for

limitations on state extraterritorial powers because

that clause at its core is concerned with

extraterritoriality.” Rosen, State Extraterritorial

Powers Reconsidered, 85 Notre Dame L. Rev. 1133,

1153 (2010); see also Laycock, Equal Citizens of Equal

and Territorial States, 92 Colum. L. Rev. 249, 290,

296-301 (1992).

11

Second, the Privileges and Immunities Clause

likewise limits a State’s ability to regulate beyond its

territorial borders. That Clause guarantees that “[t]he

Citizens of each State shall be entitled to all Privileges

and Immunities of Citizens in the several States.”

U.S. Const. art. IV, §2, cl. 1. The Clause bars

discrimination against out-of-state citizens absent a

“substantial reason” beyond “the mere fact that they

are citizens of other States.” Toomer v. Witsell, 334

U.S. 385, 396 (1948). Its aim is to place citizens of all

States “upon the same footing.” Paul v. Virginia, 75

U.S. (8 Wall.) 168, 180 (1868).

Tort liability that exceeds a State’s territorial

jurisdiction implicates that constitutional guarantee.

Again consider this context: When a State subjects

out-of-state actors to its tort standards for emissions

occurring wholly elsewhere, it imposes regulatory

burdens on nonresidents who had no voice in shaping

those standards. Those actors face liability if they do

not conform their conduct in their home States to the

forum State’s preferred rules. That is discrimination

in substance—citizens located outside Colorado are

saddled with obligations from the policy choices of a

different sovereign. The Clause does not permit a

State to subject nonresidents to such direct regulatory

burdens absent a substantial, territorially grounded

justification.

Third, the Import-Export Clause reinforces the

same limit from a different angle. That Clause

provides that no State may impose “any Imposts or

Duties on Imports or Exports” without congressional

consent. U.S. Const. art. I, §10, cl. 2. Although this

Court has confined the Clause to foreign imports only,

12

see Woodruff v. Parham, 75 U.S. (8 Wall.) 123, 133-36

(1869), the underlying concern is instructive: States

may not use their control over market access to impose

burdens on goods produced elsewhere. But see Camps

Newfound/Owatonna, Inc., v. Town of Harrison, 520

U.S. 564, 636-37 (1997) (Thomas, J., dissenting)

(“Woodruff was, in all likelihood, wrongly decided....

[T]he Constitution already affords us a textual

mechanism” that “address[es] the more egregious of

state actions discriminating against interstate

commerce.”).

This manifestation of the territorial-jurisdiction

principle is implicated when a State uses tort law to

regulate out-of-state emissions. When a State imposes

damages for conduct occurring in another State, that

operates as a de facto levy on that conduct—forcing

producers to internalize costs dictated by a foreign

sovereign or abandon the activity altogether. The

burden is regulatory in effect: it compels out-of-state

actors to conform their operations to the forum State’s

standards. That functional equivalence to an impost

raises the same concerns the Clause was designed to

prevent, particularly when one State seeks to

influence production practices beyond its borders

through the threat of liability.

Fourth, while some now question the applicability

of the dormant Commerce Clause to early territorial

jurisdiction decisions, see Nat’l Pork Producers, 598

U.S. at 376 n.1; Regan, supra, 1888, the archetypal

dormant Commerce Clause cases made clear that one

State may not “project its legislation into other States”

or “contro[l] commerce occurring wholly outside the

boundaries of a State.” Healy v. Beer Institute, Inc.,

13

491 U.S. 324, 334 (1989) (cleaned up); see also

Baldwin v. G.A.F. Seelig, Inc., 294 U.S. 511, 521

(1935) (“New York has no power to project its

legislation into Vermont.”). Dormant Commerce

Clause cases now consider hard questions about

whether in-state regulations “discriminate ... against

out-of-state

economic

interests”

or

have

“extraterritorial effects,” but all agree that the

dormant Commerce Clause precludes a State from

“directly regulat[ing] out-of-state” conduct that has

“no connection to the State.” Nat’l Pork Producers, 598

U.S. at 364, 373, 376 n.1; see also Edgar v. MITE

Corp., 457 U.S. 624, 641 (1982) (applying the dormant

Commerce Clause where a law “directly regulates”

conduct that “take[s] place across state lines, even if

wholly outside the State”) (plurality op.). After all, at

the Founding, no individual State had authority to

regulate commerce beyond its borders. The Commerce

Clause vested this nationwide regulatory power in

Congress, and its “negative” corollary simply confirms

that the States retained no such extraterritorial

commerce authority themselves.

When applied to prohibit States from directly

regulating conduct that occurs outside their territorial

borders, the dormant Commerce Clause forecloses the

use of state tort law to regulate matters like out-ofstate emissions. Imposing liability under one State’s

law for conduct occurring wholly in another State is,

in substance, an attempt to “directly regulat[e] out-ofstate” activity with “no connection to the State.” Nat’l

Pork Producers, 598 U.S. at 376 n.1 (emphasis added).

It is a projection of one State’s policy choices into

another’s territory—the very thing Healy and

Baldwin forbid. And the defect is only magnified in

14

the interstate-emissions context, where multiple

States could impose competing tort regimes on the

same conduct, subjecting actors to inconsistent

obligations and effectively placing nationwide

commerce under the control of whichever State’s law

is most restrictive.

Fifth, one application of the Fourteenth

Amendment’s Due Process Clause implicates the

territorial jurisdiction principle, barring one State’s

laws from regulating conduct occurring wholly in

another. U.S. Const. amend. XIV, §1. This Clause

operates as “an instrument of interstate federalism”

that limits a State’s lawful reach. World-Wide

Volkswagen v. Woodson, 444 U.S. 286, 294 (1980); see

also Rosen, supra, 1137-38 (“[D]ue process primarily

protects individuals from being unfairly subject to

another state’s laws.”). That limit applies to both

jurisdiction and choice-of-law—a State may apply its

own substantive law only where it has “significant

contact[s]” with the conduct at issue, such that

applying its own law to out-of-state conduct is neither

“arbitrary nor fundamentally unfair.” Phillips

Petroleum Co. v. Shutts, 472 U.S. 797, 818 (1985)

(cleaned up). Where the conduct occurred entirely in

another State, and was lawful under that State’s

regulatory regime, applying another State’s contrary

law to conduct outside its territorial boundaries is

“sufficiently arbitrary and unfair as to exceed

constitutional limits.” Id. at 822. In that

circumstance, applying forum law does not adjudicate

a local dispute—it displaces another sovereign’s policy

choices within that other sovereign’s territory.

15

The territorial jurisdiction concerns reflected in

the Due Process Clause have particular force here.

Imposing Colorado tort liability for emissions that

occurred outside of Colorado is an effort to “project

[Colorado’s] regulatory regime into the jurisdiction of

another State,” Healy, 491 U.S. at 337, and to

“infring[e] on the policy choices of other States,” BMW,

517 U.S. at 571-72. But as discussed, this Court has

foreclosed that gambit: “[A] State cannot punish a

defendant for conduct that may have been lawful

where it occurred.” State Farm, 538 U.S. at 421-22.

When the challenged conduct is lawful in the State

where it occurs, imposing liability under another

State’s law does not supplement that regime—it

overrides it. The Due Process Clause forbids that

exercise of a State’s power outside its territorial

jurisdiction.

*

Taken together, those historical sources and

constitutional provisions confirm that the doctrine of

territorial jurisdiction is not a free-floating inference

from the constitutional structure alone. It is grounded

in the preexisting law of nations and principles of

sovereignty. And it is embodied in the Constitution’s

text, where it manifests in multiple clauses that

operate in different doctrinal settings and converge on

the same limit. The Constitution did not disrupt that

well-understood baseline. It preserved the States as

coequal sovereigns, and did not expand States’

extraterritorial regulatory authority beyond what

they had before the Founding. See Cole v.

Cunningham, 133 U.S. 107, 112 (1890) (“The

constitution did not mean to confer any new power on

16

the states.”); Livermore v. Jenckes, 62 U.S. (21 How.)

126, 128-29 (1858). To the contrary, the Constitution

presupposes the absence of any such power by

individual States. See N.Y. Life Ins. Co. v. Head, 234

U.S. 149, 160-61 (1914). And if the Constitution were

to have conferred on the States a sweeping new

authority to regulate conduct beyond their borders—

authority unknown to the law of nations and

incompatible with coequal sovereignty—it would have

said so clearly. But it does not say anything about

such a new, sweeping power. So the rule that

preexisted the Founding remains in effect now—

States may govern within their borders, but they may

not govern beyond them.

B. This Court has consistently applied the

principle of territorial jurisdiction to

prevent a State from regulating conduct

in other States.

The principle that a State cannot regulate beyond

its territorial jurisdiction might be one of the “least

understood” and “most dormant” of the principles of

horizontal federalism. Energy & Env’t Legal Inst. v.

Epel, 793 F.3d 1169, 1172 (10th Cir. 2015) (Gorsuch,

J.). Even so, this Court has never seriously questioned

or doubted it. Rather, it has confirmed that a State

such as Colorado “has no power to project its

legislation into [another State] by regulating” conduct

that occurs outside of Colorado’s territorial borders.

Baldwin, 294 U.S. at 520. Indeed, this principle was

so clear that in prior litigation implicating whether a

State could directly regulate conduct within its

borders in a way that indirectly affected conduct

outside its borders, it was simply “not disputed” that

17

a State could never directly regulate conduct outside

of its borders. Id.

Over time, the principle has been called different

names, including “interstate federalism,” Fuld, 606

U.S. at 14, “comity,” Franchise Tax Bd., 587 U.S. at

245, “territorial limits” under the “horizontal

separation of powers,” Nat’l Pork Producers, 598 U.S.

at 376 n.1, and the “extraterritoriality principle.”

Regan, supra at 1885 (1987). Whatever label courts

attach to it, the underlying constitutional principle

has remained the same: A State may not legislate or

regulate conduct that falls outside its territorial

boundaries. See also Healy, 491 U.S. at 334 (a State’s

statute can “ha[ve] an impermissible extraterritorial

effect”). “The limits of state power are defined in view

of the relation of the states to each other in the

Federal Union,” Burnet v. Brooks, 288 U.S. 378, 401

(1933), so “assert[ing] extraterritorial jurisdiction ...

exceed[s] the inherent limits of the State’s power,”

Shaffer v. Heitner, 433 U.S. 186, 197 (1977).

This Court’s early decisions confirm that those

territorial limits on state power were both understood

and enforced from the beginning. In Ogden v.

Saunders, this Court explained that “when ... the

States pass beyond their own limits, and the rights of

their own citizens , and act upon the rights of citizens

of other States, there arises a conflict of sovereign

power, and a collision with the judicial powers granted

to the United States, which renders the exercise of

such a power incompatible with the rights of other

States, and with the constitution of the United

States.” 25 U.S. (12 Wheat.) 213, 369 (1827). Nor could

a State insist—absent a federally-imposed rule of

18

comity—that its own bankruptcy law be given effect

in other States. That would be “a power which no State

possessed,” or even “ever pretended to possess.” Id. at

275-76. Elsewhere the Court noted that “the

government of a particular territory[] could have no

force beyond its limits.” Strader v. Graham, 51 U.S.

(10 How.) 82, 94 (1850). And the Court held that a

State’s “[l]aws have no force of themselves beyond the

jurisdiction of the state which enacts them, and can

have extraterritorial effect only by the comity of other

states”—a principle that derived from “[t]he general

rules of international comity” well “before the

American Revolution.” Huntington v. Attrill, 146 U.S.

657, 669 (1892).

As a “consequence of territorial limitations on the

power of the respective States,” Hanson v. Denckla,

357 U.S. 235, 251 (1958), “[n]o State can legislate

except with reference to its own jurisdiction,”

Bonaparte v. Tax Court, 104 U.S. 592, 594 (1881). And

no state “can impose its own legislation” or “enforce its

own policy upon the other[s].” Kansas, 206 U.S. at 98.

It would be “impossible to permit the statutes of [a

State] to operate beyond the jurisdiction of that State

… without throwing down the constitutional barriers

by which all the States are restricted within the orbits

of their lawful authority.” N.Y. Life Ins., 234 U.S. at

160-61. Indeed, this Court has “long recognized that

the Constitution restricts a State’s power to reach out

and regulate conduct that has little if any connection

with the State’s legitimate interests.” Mallory v.

Norfolk S. Ry. Co., 600 U.S. 122, 154 (2023) (Alito, J.,

concurring in part). This principle is “an ‘obviou[s]’

and ‘necessary result’ of our constitutional order,” and

its origin is not “confined to any one clause or section,

19

but is expressed in the very nature of the federal

system that the Constitution created and in numerous

provisions that bear on States’ interactions with one

another.” Id. (quoting N.Y. Life Ins., 234 U.S. at 161).

Applying the principle of territorial jurisdiction,

this Court has consistently prevented States from

extending their legislative or regulatory reach beyond

their own borders. Consider Bonaparte. There, a

person who owned securities that were exempt from

taxation by the issuing States (New York,

Pennsylvania, and Ohio) argued that those securities

were also exempt from taxation once moved to and

registered in Maryland. This Court resolved the

question in a single sentence: “No State can legislate

except with reference to its own jurisdiction.” Id. at

594. That is, the tax laws of New York, Pennsylvania,

and Ohio provided no tax exemption for Maryland’s

tax laws. See Regan, supra, 1887.

So too in Edgar v. MITE Corp., 457 U.S. 624

(1982). There, the State of Illinois enacted a statute

regulating corporate takeover bids. This statute was

“written in such a way that it could apply to target

corporations that were not incorporated in Illinois and

that had no Illinois shareholders.” Regan, supra,

1897. A plurality of the Court found that this statute

had a “sweeping extraterritorial effect, since it

“directly regulates transactions which take place

across state lines, even if wholly outside the State of

Illinois,” and “would apply even if not a single one of

[a company]’s shareholders were a resident of

Illinois.” Edgar, 457 U.S. at 641-42 (plurality op.).

20

And more recently, this Court considered the

territorial jurisdiction principle in Healy v. Beer

Institute, Inc., 491 U.S. 324 (1989). There, a

Connecticut

law

required

out-of-state

beer

distributors to affirm that the wholesale price of their

products sold into Connecticut was no higher than the

price of the same goods sold into any other state. This

Court found that statute violated the territorial

jurisdiction principle, holding that “[a] state statute

that directly controls commerce occurring wholly

outside the boundaries of a State exceeds the inherent

limits of the enacting State’s authority and is invalid

regardless of whether the statute’s extraterritorial

reach was intended by the legislature.” Id. at 336.

Taken together, these decisions confirm that a

State may not legislate except with respect to conduct

within its own territorial borders or that directly

touches its territorial boundaries. And a State may

not achieve indirectly—through statutes with

sweeping reach or pricing mandates—what it cannot

do directly.

To that end, the principle of territorial jurisdiction

applies equally to a State’s direct legislation and to

lawsuits invoking a State’s common law. After all, a

“state[’s] power may be exercised as much by a jury’s

application of a state rule of law in a civil lawsuit as

by a statute.” BMW, 517 U.S. at 572 n.17. Awarding

damages is a “potent method of governing conduct and

controlling policy,” Kurns v. R.R. Friction Prods.

Corp., 565 U.S. 625, 637 (2012) (cleaned up), so a State

“may not impose economic sanctions on violators of its

laws with the intent of changing the tortfeasors’

lawful conduct in other States,” BMW, 517 U.S. at 572.

21

Accordingly, the principle of territorial jurisdiction

also bars a State from using its common law to

regulate out-of-state conduct.

This principle of territorial jurisdiction and its

limits on a State’s regulatory reach resolves this case.

Boulder County’s lawsuit would do exactly what the

Constitution forbids: Regulate conduct occurring

wholly in other States and lawful under those States’

own laws. The Constitution does not permit one State

to act that way, to exclude or burden out-of-state

actors based on its own preferences, or to directly

impose its will on conduct beyond its jurisdiction.

C. This Court’s precedent on interstate

environmental disputes confirms that no

single State may govern conduct beyond

its borders.

Long before the modern regulatory state, this

Court confronted the recurring problem of two

sovereign States fighting over interstate pollution.

Each time the Court considered such a case, it applied

the doctrine of territorial jurisdiction and reached the

same conclusion—this sort of interstate dispute

cannot be resolved by the law of any one State. That

conclusion rested on the Constitution’s allocation of

sovereign power and on the conclusion that letting a

single State’s policy dominate another’s is fundamentally inconsistent with the equal dignity of every

member State in the Union. Thus, for well “over a

century,” this Court has understood the need for

federal resolution of such disputes and “has applied

federal law to disputes involving interstate air or

water pollution.” City of New York v. Chevron Corp.,

22

993 F.3d 81, 91 (2d Cir. 2021) (collecting Supreme

Court cases).

1. This Court’s earliest treatment of interstate

environmental disputes established the baseline that

a single State’s law cannot regulate environmental

disputes that involve conduct occurring outside its

territorial jurisdiction and that is lawful where it

occurs. The “cardinal rule, underlying all the relations

of the states to each other, is that of equality of right.”

Kansas, 206 U.S. at 97. No state can “impose its own

legislation” or “enforce its own policy upon the

other[s].” Id. at 95, 97. So when it comes to regulating

things that occur in multiple States, either Congress

or “interstate common law” must provide “the rule

which shall control.” Id. After all, “[t]he rule of

decision” for matters involving multiple states “has

always been ... what we now know as the federal

common law.” Minnesota v. Am. Petroleum Inst., 63

F.4th 703, 718 (8th Cir. 2023) (Stras, J., concurring);

see also Kansas, 206 U.S. at 98 (identifying applicable

law as “what may not improperly be called interstate

common law”).

One year earlier, in Missouri v. Illinois, 200 U.S.

496 (1906), Missouri sued to enjoin the discharge of

sewage into an Illinois river that flowed downstream

into Missouri waterways. This Court did not ask (or

decide) whether Missouri or Illinois substantive law

governed. Missouri pleaded a nuisance claim much

like the nuisance claim here—a bare allegation that

some abstract action taken inside one State had

somehow or other injured residents in another State.

See id. This Court declined to defer to Missouri’s

application of its own nuisance law. Instead, it noted

23

that no one pretended that Missouri’s claim of

“nuisance” was the same as the “simple kind that was

known to the older common law.” Id. at 522. It then

ruled that Missouri’s nuisance claim lacked causation

or proof of injury. Id. at 522-26.

Since Missouri’s claim in that case was unlike a

normal nuisance tort claim, lacking either direct

causation or injury, it amounted to the kind of claim

where one State sought to hold another State

accountable for a generalized harm. And the Court did

acknowledge that in theory, if “a nuisance” was

“created by a state upon a navigable river like the

Danube,” it would have “amount[ed] to a casus belli

for a state lower down, unless removed.” Id. at 520-21.

Under the law of nations, such a dispute would be

“settled by treaty or by force.” Kansas, 206 U.S. at 98.

But since the Constitution suspends the ability of

States to either wage war upon each other or enter

into treaties without congressional approval, such

disputes must be settled by this Court. Id. at 97

(“Force, under our system of government, is

eliminated. The clear language of the Constitution

vests in this court the power to settle those disputes.”).

Nor was this principle limited to suits between

States. One year after Missouri, this Court applied the

same framework to a case involving interstate air

pollution. In Georgia v. Tennessee Copper Co., 206

U.S. 230 (1907), Georgia sought to enjoin a Tennessee

company from “discharging noxious gas” across the

state line. Id. at 236. There, the Court held that

Georgia was entitled to seek “specific relief” rather

than “give up quasi-sovereign rights for pay.” Id. at

237. But more important, as relevant here, is what the

24

Court did not do. It did not apply Georgia law to the

Tennessee defendant. Nor did it apply Tennessee law

to the dispute. Instead, the Court applied a body of

federal equity principles derived from the logic of

interstate sovereignty itself, because “the forcible

abatement of outside nuisances” is not a power any

single state can constitutionally claim. Id.

Those early decisions reflected a consistent

understanding that when States’ sovereign interests

collide across territorial lines, neither States’ laws

applied and neutrality requires a federal rule. Hence

this Court declined to apply “municipal law” to resolve

interstate water disputes in Connecticut v.

Massachusetts, 282 U.S. 660 (1931), and instead

applied principles of “equality of right” derived from

“federal, state and international law” alike. Id. at 670.

It did the same in New Jersey v. New York, 283 U.S.

336 (1931), recognizing that every state has “real and

substantial interests” in shared natural resources and

that “[d]ifferent considerations come in when we are

dealing with independent sovereigns” and also with

“the quasi-sovereignties bound together in the Union.”

Id. at 342. In Iowa v. Illinois, 147 U.S. 1 (1893), the

Court rejected the views of dueling state courts over

competing claims to river rights in favor of the

“equality” principle derived from the neutral federal

rule. Id. at 13. And in Hinderlider v. La Plata River &

Cherry Creek Ditch Co., 304 U.S. 92 (1938), the Court

again confirmed that this territorial-jurisdiction

principle applies to lawsuits involving private parties

and environmental disputes. It held that the

apportionment of interstate water “is a question of

federal common law upon which neither the statutes

25

nor the decisions of either State can be conclusive.” Id.

at 110.

The cases speak with one voice. Whenever this

Court has confronted environmental or conservation

disputes touching the sovereign prerogatives of

multiple States, it has never let one State project its

law beyond its borders and dictate the rules of decision

for the Nation as a whole. That restraint reflects the

core principle implicated here—no State may wield its

law extraterritorially to regulate conduct and

interests belonging to its sister States.

2. Consistent with those cases, this Court’s

decision in Milwaukee I and its progeny make clear

that a single State’s law can never govern interstate

pollution claim. And the later displacement of federal

common law still does not open the door for States to

regulate interstate emissions through their own law.

In Illinois v. City of Milwaukee, 406 U.S. 91 (1972)

(“Milwaukee I”), Illinois sought to abate sewage

discharges into Lake Michigan by Wisconsin

municipalities. This Court ruled that the interstate

“nature of the problem” implicated the interests of

multiple sovereign States and thus could not be

resolved by the law of any single State. Id. at 103 n.5.

In “deal[ing] with air and water in their ... interstate

aspects,” the “overriding federal interest” required “a

uniform rule of decision.” Id. at 103, 105 n.6. Illinois

could not be asked “to submit to whatever might be

done,” id. at 104 (cleaned up), but neither could

Wisconsin municipalities be subjected to Illinois law.

26

The Court made clear that the dispositive point

was not merely geographic but structural. Lake

Michigan is “bounded ... by four States,” one of which

happened to be permitting the pollution that the other

opposed. Id. at 105 n.6. When the policies and wills of

sovereign States are set on a collision course, the

“nature of the problem” created an interstate conflict

that required a neutral arbiter—namely, federal law.

Id. at 103 n.5. State law cannot provide that

neutrality. Only federal law—“not the varying

common law of the individual States”—can furnish “a

basis for dealing in uniform standard with the

environmental rights of [each] State.” Id. at 107 n.9

(cleaned up).

Milwaukee I’s logic survived Congress’s later

regulation of environmental matters. In City of

Milwaukee v. Illinois, 451 U.S. 304 (1981)

(“Milwaukee II”), the Court held that the Clean Water

Act displaced the federal common-law remedy

recognized in Milwaukee I. But at the same time, the

Court confirmed that displacing the remedy did not

eliminate the structural principle necessitating it in

the first place. Federal substantive law must apply to

interstate environmental disputes, since “state law

cannot be used” to neutrally decide between the

competing interests of sovereign States. Id. at 313 &

n.7. Even after “new federal laws and new federal

regulations” have been enacted and replace the

“federal common law of nuisance,” id. at 314 (cleaned

up), States are still “not left free to develop their own

doctrines” in the areas where state law remains

inherently unable to resolve interstate disputes,

Banco Nacional de Cuba v. Sabbatino, 376 U.S. 398,

426 (1964).

27

The Seventh Circuit applied that this exact

principle in Illinois v. City of Milwaukee, 731 F.2d 403

(7th Cir. 1984) (“Milwaukee III”). Illinois argued that

once the Clean Water Act displaced the federal

common law that controlled in Milwaukee I, “Illinois

law must again control.” Id. at 406. The Seventh

Circuit rejected that contention outright: “[T]he state

claiming injury cannot apply its own state law to outof-state discharges.” Id. at 410. And for good reason.

“The very reasons the [Supreme] Court gave for

resorting to federal common law in Milwaukee I are

the same reasons why ... federal law must govern” the

interstate pollution question still. Id. at 410-11.

The Seventh Circuit’s correct reasoning squarely

forecloses the notion, embraced by the Colorado

Supreme Court, that where federal common law once

existed but was later replaced by federal statute, a

single State’s common law can snap back into the void

and still have effect. See App.17a. “[S]tate law does not

suddenly become competent to address issues that

demand a unified federal standard simply because

Congress ... displace[d] a federal court-made standard

with a legislative one.” City of New York, 993 F.3d at

98; accord App.26a (Samour, J., dissenting). As

Justice Samour correctly recognized in dissent below,

this Court’s precedents collectively establish that

“simply because federal common law relating to” this

issue “has been displaced by statute doesn’t mean that

the conditions that made state law inappropriate to

govern these claims in the past have vanished.”

App.26a. And “Congress’s decision to displace federal

common law and to take control of this area did not

suddenly render state law competent to regulate

interstate and international air pollution.” Id.

28

3. This Court’s most recent examination of

interstate emissions—in Am. Electric Power Co. v.

Connecticut, 564 U.S. 410 (2011) (“AEP”)—reaffirmed

the same environmental territorial-jurisdiction

limitation announced Missouri, Kansas, Milwaukee

II, and their progeny. “[S]uits brought by one State to

abate pollution emanating from another State” are

“meet for federal law governance.” Id. at 421-22.

“[H]ere,” where States brought public nuisance claims

against private energy companies for their alleged

greenhouse gas emissions, “borrowing the law of a

particular State would be inappropriate” to resolve

such interstate disputes. Id. at 422.

AEP forecloses the theory embraced by the

Colorado Supreme Court below. While in AEP the

Court left open (in dicta) the theoretical possibility of

some state-law nuisance claims, the Court noted only

that the Clean Water Act “does not preclude” suits

brought under “the law of the source State.” Id. at 429

(quoting Int’l Paper Co. v. Ouellette, 479 U.S. 481, 489

(1987)). But this lawsuit was not brought under “the

law of the source State.” Id. Boulder County instead

sued under Colorado law—the law of the allegedly

affected State, not the source State.

The type of claim AEP left open—an intrastate

dispute governed by the law of the source State—

never required federal common law in the first place.

Interstate disputes like this one, by contrast, have

never been left to the law of a single State. Ouelette

confirms the point. There, this Court held that federal

law preempted one State trying to enforce its state

nuisance law against an out-of-state emissions source,

even though federal law did not preempt state actions

29

brought under the law of the source state. Ouelette,

479 U.S. at 497. Allowing every State to apply its own

emissions laws nationwide would result in regulatory

“uncertainty” and “chaotic confrontation between

sovereign states.” Id. at 496 (cleaned up). If energy

producers like Suncor must conform their conduct to

the competing tort regimes of every State claiming

downstream effects from global operations, “[t]he

result would be” an impossible “patchwork of

standards” that would harm “industry and the

environment alike.” North Carolina ex rel. Cooper v.

TVA, 615 F.3d 291, 296 (4th Cir. 2010) (Wilkinson, J.);

see also City of New York, 993 F.3d at 91; App.25a, 28a

(Samour, J., dissenting).

*

Colorado law may govern “persons and property

within the limits of its own territory.” Hoyt v. Sprague,

103 U.S. 613, 630 (1880). But Boulder County seeks to

directly regulate conduct that occurs outside those

limits. There is no historical analogue for what

Boulder is trying to do, because this Court’s cases

have never permitted it. It should not start now.

II. Boulder County’s Lawsuit Violates

Doctrine of Territorial Jurisdiction.

the

As described, the doctrine of territorial jurisdiction

is grounded in the Constitution’s text, the inherent

structure of horizontal federalism and State

sovereignty, and this Court’s prior precedents on

interstate disputes. Its rule is straightforward: “No

State can legislate except with reference to its own

jurisdiction.” Bonaparte, 104 U.S. at 594. No State

30

“can impose its own legislation” or “enforce its own

policy upon the other[s].” Kansas, 206 U.S. at 95, 97.

And each State’s “sovereign authority is bounded by

the States’ respective borders.” Fuld, 606 U.S. at 14.

Boulder County’s lawsuit violates every one of these

commands.

Here, Boulder County seeks to regulate conduct

that occurred almost entirely outside Colorado.

Suncor is headquartered in Canada. ExxonMobil is

headquartered in Texas. Their extraction and

production activities span the globe, and they operate

legally under the laws of each jurisdiction where they

operate.

Colorado “has no power to project its legislation”

into those jurisdictions. Baldwin, 294 U.S. at 521. And

labeling its desired remedy “compensat[ion],”

“remediation,” and “abatement,” App.50a, rather than

“regulation,” does not cure the constitutional defect.

State power is “exercised as much by a jury’s

application of a state rule of law in a civil lawsuit as

by a statute,” BMW, 517 U.S. at 572 n.17, and

Colorado cannot “punish a defendant for conduct that

may have been lawful where it occurred,” State Farm,

538 U.S. at 421-22.

The implications of affirming the Colorado

Supreme Court’s jurisdiction extend far beyond

energy policy. Doing so would license a form of

interstate regulatory warfare that will cripple every

industry to the detriment of consumers nationwide. If

one State may use its tort law to impose liability on

out-of-state energy producers for their global

operations, every State may do the same. Colorado

31

could impose tort liability on out-of-state

manufacturers of gas stoves and furnaces for alleged

abstract air quality harms—effectively forcing

manufacturers to stop producing appliances that are

legal, preferred, and widely sold in every other state.

Consumers in other states would lose access to

cheaper, reliable products because Colorado decided

to litigate them out of existence.

Nor are the implications of affirming the Colorado

Supreme Court’s judgment limited to environmental

issues. If Colorado can impose its law on conduct that

occurred lawfully in other States, a state with strict

usury laws could impose tort liability on out-of-state

consumer lenders for “predatory” lending to customers

who voluntarily sought those products online. Even

though such consumer lenders would be operating

lawfully under their home States’ regulations,

consumers in all States with limited banking

infrastructure would lose access to the only credit

available to them. Or a state like California could

impose tort liability on every out-of-state firearms

manufacturer and dealer, regardless of whether those

firearms—lawful under the laws of every other

State—ever found their way into California.

Each of those scenarios is constitutionally

indistinguishable from what Boulder County

attempts here. No State “can impose its own

legislation” or “enforce its own policy upon the

other[s],” Kansas, 206 U.S. at 95, 97, and no State can

“impose economic sanctions on violators of its laws

with the intent of changing the tortfeasors’ lawful

conduct in other States.” BMW, 517 U.S. at 572. If that

principle means anything, it means that Colorado

32

cannot directly regulate the lawful fossil fuel activities

that occur outside of its territorial borders. And it

means that Boulder County cannot do through

nuisance litigation what Colorado could never do

through legislation.

CONCLUSION

The judgment of the Colorado Supreme Court

should be reversed.

Respectfully submitted,

Tyler R. Green

Counsel of Record

CONSOVOY MCCARTHY PLLC

222 S. Main St., 5th Fl.

Salt Lake City, UT 84101

(703) 243-9423

tyler@consovoymccarthy.com

Cody Ray Milner

CONSOVOY MCCARTHY PLLC

1600 Wilson Blvd., Ste. 700

Arlington, VA 22209

Counsel for Amicus Curiae

Dated: May 2026