Supreme Court Limits EPA’s Flexibility in Cross-State Air Pollution Enforcement

New Legal Hurdle for EPA’s Air Enforcement

In an 8–0 ruling, the U.S. Supreme Court has dealt a procedural blow to the EPA’s efforts to curb cross-state air pollution. The decision adds a new layer of complexity to how the agency enforces its “good neighbor” rules under the Clean Air Act, which target emissions that drift from one state into another.

The Court found that when EPA disapproves of a state’s individual air quality plan, the appropriate venue for legal challenges is not the D.C. Circuit, as EPA argued, but regional courts of appeals. The opinion, authored by Justice Clarence Thomas, holds that these disapprovals are based on state-specific facts and should be reviewed locally. Justice Alito did not participate in the decision.

Implications for EPA’s 2023 Good Neighbor Plan

The ruling stems from EPA’s 2023 implementation of a federal good neighbor plan covering 23 states. EPA rejected 21 state-submitted plans in a single action and finalized a federal version to reduce ozone-forming emissions from industrial sources. EPA treated the rejection as a single national rule, subject to centralized review in the D.C. Circuit.

The Supreme Court disagreed. It reversed a Tenth Circuit ruling and held that each state’s disapproval should be litigated in its respective appellate court.

This outcome complicates the enforcement landscape. Legal battles may now unfold in multiple courts at once, introducing delay, added cost, and potential for conflicting judgments.

A Win for Procedural Access, A Risk for Policy Cohesion

Supporters of the ruling, including several states and industry groups, praised it as a victory for procedural fairness. They argue it provides states a better opportunity to challenge EPA decisions based on local context.

But environmental advocates warn that the change weakens coordinated federal oversight. The fragmented litigation path could reduce the effectiveness of pollution control in downwind states, where ozone levels already threaten public health.

The Biden-era rule was already on hold due to a 5–4 stay issued by the Supreme Court last year. The Trump administration has since signaled its intent to roll it back entirely.

What This Means for Industry

The ruling introduces both relief and uncertainty for the industry. With the federal rule paused, companies may face fewer immediate compliance obligations. However, the risk of inconsistent standards across states could increase compliance costs in the long run.

For businesses with operations in multiple states, this could signal the beginning of a more fragmented regulatory environment for ozone emissions. Companies may need to monitor regional litigation and prepare for shifting requirements on a state-by-state basis.

EPA’s Authority Intact, but the Road Is Harder

While the ruling does not alter EPA’s legal authority under the Clean Air Act’s good neighbor provision, it reshapes the road ahead. Coordinated enforcement may now require piecemeal litigation and rulemaking, slowing progress and increasing the administrative burden for all parties involved.

EPA has said it is reviewing the decision. The agency’s next moves will be closely watched as it seeks to balance federal oversight with the new constraints on its enforcement strategy.