Supreme Court Decides Oklahoma v. Environmental Protection Agency

On June 18, 2025, the Supreme Court decided Oklahoma v. Environmental Protection Agency, No. 23-1067, holding that the EPA’s disapproval of Oklahoma and Utah’s state implementation plans under the Clean Air Act are locally or regionally applicable actions reviewable in a regional Circuit. 

In 2015, the EPA revised the national ambient air quality standards. As a result, each State was required to submit a state implementation plan (SIP) detailing how it would comply with the “Good Neighbor” provisions of the Clean Air Act and avoid interfering with other States’ air quality standards compliance. The EPA determined 21 States’ SIPs were inadequate in one omnibus Federal Register rule. 

For any “action” under the Clean Air Act, “nationally applicable” challenges must be heard in the D.C. Circuit and “locally and regionally applicable challenges” must be heard in regional Circuits unless the action has a “nationwide scope and effect.”

States and industry petitioners challenged the SIP disapprovals in five different regional Circuits. Four of the circuits held that regional review was proper, but the Tenth Circuit disagreed and transferred the suits from Oklahoma and Utah to the D.C. Circuit.

In an 8-0 decision, the Supreme Court reversed the Tenth Circuit, allowing Oklahoma and Utah’s challenges to proceed in regional Circuits. The Court held that the question boiled down to what constitutes an “action” under the Clean Air Act. The Court determined that the disapproval of each SIP was its own “action.” The EPA’s disapproval of the Oklahoma and Utah SIPs were therefore individual actions, separate from the disapproval of the other 19 SIPs. When viewed as individual actions, the disapproval of the Oklahoma and Utah SIPs were indisputably local or regional in nature with no nationwide scope or effect and could therefore be heard in regional Circuits. 

Justice Thomas delivered the opinion, which Justices Sotomayor, Kagan, Kavanaugh, Barrett, and Jackson joined. Justice Gorsuch filed an opinion concurring in the judgment, which Chief Justice Roberts joined. Justice Alito took no part in the consideration or decision of the case.