E.P.A. v. EME Homer City Generation, L.P.
The Court upheld the EPA's Cross-State Air Pollution Rule, ruling that the agency could require upwind states to cut smokestack pollution based on cost-effectiveness rather than a strict state-by-state proportional formula, and that the EPA did not have to give states a second chance to write new state plans after setting pollution budgets.
The decision preserves a major federal tool for controlling air pollution that drifts across state lines, reinforcing the EPA's authority to fill gaps left by ambiguous statutory language when Congress hasn't spelled out exactly how to divide pollution-control burdens among states.
How it got here: The D.C. Circuit vacated the Transport Rule entirely, and the EPA and environmental groups asked the Supreme Court to review that decision.
The Case in Depth
What happened
Air pollution from power plants in one state often drifts into neighboring states, making it hard for those downwind states to meet federal air-quality standards. The EPA's Cross-State Air Pollution Rule (Transport Rule) required 27 upwind states to cut nitrogen oxide and sulfur dioxide emissions using a formula based partly on how cheaply those reductions could be achieved. States, industry groups, and labor groups challenged the rule as exceeding EPA's authority under the Clean Air Act's Good Neighbor Provision.
The question before the Court
Could the EPA make upwind states cut pollution based on how cheaply they could reduce it, instead of strictly in proportion to how much pollution each state actually sent downwind?
The Court's answer
Yes — the Court ruled that the EPA could use a cost-based method to divide up pollution-reduction obligations among upwind states, rather than being forced to use a strict proportional formula tied only to each state's share of the pollution. The Good Neighbor Provision doesn't say how to split responsibility when several states' combined pollution pushes a downwind state over the legal limit, so the Court treated this as a gap Congress left for EPA to fill, and deferred to EPA's reasonable choice under the Chevron framework.
The Court also ruled that EPA did not have to give states a second opportunity to submit their own pollution-control plans after calculating each state's emissions budget; the statute's deadlines for state plans and federal takeover plans are strict, and EPA could proceed straight to a federal plan once it found a state's plan inadequate.
Curious how the Court got there? See the step-by-step legal reasoning →
Why it matters
Power plants and industrial polluters in upwind states must keep meeting emissions budgets set by the EPA's cost-based formula rather than a purely proportional one, affecting compliance costs nationwide. Downwind states and their residents retain a functioning federal mechanism for curbing pollution blown in from other states, while the ruling also reaffirms broad EPA discretion to interpret ambiguous provisions of the Clean Air Act.
What changes now
The case is sent back to the D.C. Circuit for further proceedings consistent with the Court's ruling, including consideration of an argument about states whose plans EPA had previously approved that the lower court had not yet addressed. The Transport Rule itself remains in effect, and states can still bring individual challenges if they believe EPA's formula forced them to cut emissions below the significance threshold or beyond what's needed for downwind attainment.
What this does not decide
The Court did not decide two additional arguments left for the lower court on remand: whether EPA properly converted certain states' prior SIP approvals into disapprovals, and any individual, as-applied challenges claiming a specific state was forced to cut emissions below the one-percent threshold or beyond what downwind attainment required.
Concurrences and dissents
Dissent — Justice Scalia
Justice Scalia argued the Good Neighbor Provision plainly ties each upwind state's responsibility to the actual amount of pollution it contributes, not to how cheaply it can be reduced, so EPA's cost-based approach rewrites the statute rather than filling a genuine gap. He also argued the Clean Air Act's cooperative-federalism structure required EPA to tell states what 'significant' contribution meant before demanding they submit compliant plans, and that EPA's past practice of doing exactly that showed the majority's position was an abuse of discretion. He would have affirmed the D.C. Circuit's vacatur of the rule.
How the Court got there
The legal reasoning, step by step
- The Court first held that nothing in the Clean Air Act requires EPA to give states a second chance to submit implementation plans after EPA calculates each state's pollution-reduction obligations; the statute's deadlines for plan submission and federal takeover are absolute and leave no room for an unwritten grace period.
- Because EPA had earlier given states time to allocate emission budgets under prior rules, the Court asked whether skipping that step this time was arbitrary; under the standard requiring agencies to explain policy changes reasonably, the Court found EPA's explanation adequate because a federal appeals court had told EPA to act quickly to fix its earlier rule.
- Turning to the merits of the pollution-allocation method, the Court applied Chevron deference, the doctrine that courts defer to a reasonable agency interpretation when a statute is ambiguous and Congress has not directly addressed the issue.
- The Court found the Good Neighbor Provision does not specify how to divide responsibility for pollution among multiple contributing upwind states when their combined pollution exceeds the amount that must be eliminated, calling this a gap for EPA to fill.
- The Court rejected the proportional-reduction approach as unworkable in practice because a state's proportionate share differs across different downwind locations, whereas EPA's cost-based method reasonably resolved the allocation problem in both an efficient and equitable manner.
- Because EPA's approach was a permissible reading of an ambiguous statute and only rarely produced any excess or insufficient reductions, the Court concluded that any misapplication in specific instances could be challenged case-by-case rather than requiring the whole rule to be thrown out.
Doctrinal impact
Cases affected by this decision
Reaffirms Chevron U. S. A. Inc. v. Natural Resources Defense Council, Inc. (467 U. S. 837)
The Court relies on Chevron's framework to defer to EPA's reasonable interpretation of the ambiguous Good Neighbor Provision.
Distinguishes Whitman v. American Trucking Assns., Inc. (531 U. S. 457)
The Court distinguishes this case, saying its bar on considering costs doesn't apply because the Good Neighbor Provision isn't as absolute as the provision there.