Ohio v. Environmental Protection Agency
The Supreme Court paused the EPA's Good Neighbor Plan, an air-pollution rule requiring upwind states to cut ozone emissions that drift into neighboring states, while a legal challenge plays out in a lower court.
The 5-4 ruling halts the rule against the remaining states and industry groups subject to it — potentially for years — because the Court found the EPA likely acted unlawfully when it pressed ahead with a plan designed for 23 states after courts blocked its application to more than half of them.
How it got here: Applicants challenged the EPA's rule in the D.C. Circuit and asked that court to pause enforcement while the appeal proceeded; after the D.C. Circuit denied relief, they brought emergency stay applications to the Supreme Court.
The Case in Depth
What happened
The EPA issued a federal air-quality rule — the Good Neighbor Plan — requiring 23 upwind states to reduce ozone-forming emissions that drift into neighboring downwind states. The rule was designed assuming all 23 states would participate and chose its emissions-control requirements based on that combined group. Before the rule took effect, courts paused EPA's rejection of 12 states' own pollution plans, effectively blocking the federal rule from applying to those states and leaving it covering less than 30% of the originally targeted emissions. The remaining states and industry groups argued the EPA never explained whether its emissions limits still made sense with so many states gone.
The question before the Court
Can states and companies get a court order pausing the EPA's "Good Neighbor Plan" air-pollution rule — designed assuming all 23 targeted states would participate — after courts blocked its application to more than half of those states?
The Court's answer
Yes — the Court paused enforcement of the EPA's Good Neighbor Plan while the legal challenge proceeds in the D.C. Circuit. The stay test requires the Court to weigh four factors, but because both sides had strong arguments about harm and fairness, the outcome turned on who was likely to win in the end.
The Court concluded the states and companies were likely to win on their claim that the EPA acted arbitrarily. The EPA designed its plan assuming all 23 states would participate and used that assumption to determine which emissions-control measures were cost-effective. When courts blocked the plan's application to more than half the states, a basic question arose: did the cost-effectiveness analysis still hold for the much smaller remaining group? Commenters had raised this exact concern during the public comment period, but the EPA's only response was a severability clause saying the plan would continue no matter how many states remained — without ever explaining why the emissions limits would still make sense with far fewer participants. Ignoring that core question is the kind of failure the law's "arbitrary and capricious" standard is designed to catch.
Curious how the Court got there? See the step-by-step legal reasoning →
Why it matters
Downwind communities counting on cleaner air from the Good Neighbor Plan will not see those benefits while the litigation continues. Meanwhile, the upwind states and industries that remain covered are relieved — temporarily — of compliance obligations that applicants said could cost hundreds of millions to billions of dollars. The outcome of the D.C. Circuit appeal will determine whether those obligations ever take effect.
What changes now
The Good Neighbor Plan cannot be enforced against any of the applicant states or industry groups while their challenge is pending before the D.C. Circuit and, if they seek it, the Supreme Court. If the D.C. Circuit rules for the applicants, the rule could be sent back to the EPA for a new explanation or revised plan. If the D.C. Circuit rules for the EPA, the stay will dissolve and enforcement could resume. This order is temporary and does not decide the rule's ultimate validity.
What this does not decide
The Court does not decide whether the Good Neighbor Plan is ultimately lawful — only that enforcement is paused while appeal continues. It does not decide whether EPA's individual rejections of state pollution plans were valid, and it explicitly declined to address other legal theories the applicants raised beyond the core failure-to-explain claim.
Concurrences and dissents
Dissent — Justice Barrett
Justice Barrett argued the Court granted emergency relief based on a legal theory the applicants barely briefed and that largely emerged at oral argument. She contended the EPA's cost-effectiveness methodology relied on nationwide industry data, not on any particular set of states, so the concern the majority credited was not an 'important aspect' the agency was required to address. She also identified two significant procedural barriers: the Clean Air Act bars challengers from raising in court objections that were not specifically raised in public comments, and the Act's strict harmless-error rule would likely block relief even if there were a procedural flaw. She would have denied the stay.
How the Court got there
The legal reasoning, step by step
- The Court applied the four-factor framework for emergency stays from Nken v. Holder (2009): (1) likelihood of success on the merits, (2) irreparable harm without a stay, (3) substantial harm to others if the stay is granted, and (4) the public interest. No single factor is decisive; the Court weighs them together.
- Both sides had compelling arguments on factors two through four. The EPA pointed to real air-quality benefits for people in downwind states. The states and companies countered that complying with a likely unlawful rule would cost them hundreds of millions — potentially billions — of dollars that could never be recovered, and would impair their sovereign authority over their own industries. Because the equities were closely balanced, the case hinged on factor one: who was likely to win.
- The applicable legal standard for factor one is the 'arbitrary and capricious' test: agency rules must be both 'reasonable' and 'reasonably explained,' and agencies cannot ignore 'an important aspect of the problem' (drawn from State Farm, a 1983 decision that remains the benchmark for this kind of review).
- EPA's Good Neighbor Plan was built on a specific analytical foundation — a 'knee in the curve' calculation that identified the point at which further emissions-control spending stops producing meaningful air-quality improvements, and used that point to set a uniform cost level for all 23 covered states. That calculation treated the 23-state group as a whole. During the public comment period, commenters warned that if some states dropped out, the cost-effectiveness math might shift — and EPA would need to redo its analysis.
- When courts ultimately blocked the rule from applying to 12 of the 23 states — covering more than 70% of the emissions EPA had planned to address — that warning proved well-founded. Yet EPA's only response in its final rule was a severability clause saying the plan would continue regardless; it never explained why its cost-effectiveness conclusions would remain valid for a much smaller and different group of states.
- Because EPA was on notice of this concern from public comments and still failed to address it substantively, the Court found the final rule was likely 'not reasonably explained' and that EPA had ignored an important aspect of the problem — making the states and companies likely to succeed in having the rule overturned. The Court declined to address the three alternative arguments EPA raised, and also declined to adopt the dissent's analysis — which EPA itself had not advanced — because courts ordinarily do not adopt arguments the parties chose not to make.