Decision Alert: Supreme Court Clarifies Venue For Environmental Challenges

In a 6-2 decision authored by Justice Thomas, the Supreme Court held in consolidated cases Oklahoma v. EPA and PacifiCorp v. EPA that the Environmental Protection Agency (EPA)'s disapprovals of 21 individual state implementation plans (SIPs) under the Clean Air Act (CAA) are "locally or regionally applicable" actions, and, as such, must be challenged in their respective regional circuit courts—even when the EPA publishes them in a single, consolidated Federal Register notice.

As summarized in our April issue, in 2025, the EPA disapproved the SIPs, finding that they failed to meet the "good neighbor" provision of the CAA, which requires states to prevent their emissions from affecting air quality in downwind states. The EPA grouped these disapprovals in one Federal Register notice. When affected states and industry stakeholders filed suits in various regional circuits, the EPA successfully argued in the Tenth Circuit that the consolidated publication rendered the