CEI files amicus brief urging Supreme Court to review EPA’s particulate matter standards

On October 2, 2026, CEI joined the Committee for a Constructive Tomorrow, the Energy & Environment Legal Institute, the Heartland Institute, and Heartland Impact in an amicus brief supporting the petitions for certiorari filed by Kentucky and other states as well as the US Chamber of Commerce. The brief was filed at the US Supreme Court in Commonwealth of Kentucky, et al. v. EPA, et al. and Chamber of Commerce, et al. v. EPA, et al.

The cases challenge a DC Circuit decision upholding EPA’s 2024 off-cycle revision of the National Ambient Air Quality Standards (NAAQS) for fine particulate matter, commonly known as PM2.5. The rule reduced the annual PM2.5 standard by 25 percent — from 12 to 9 micrograms per cubic meter — without completing the “thorough review” prescribed by the Clean Air Act. EPA later acknowledged that the 2024 rule was the first NAAQS revision in the statute’s history not preceded by a completed thorough review.

The rule’s consequences are national. It tightens permitting requirements and may constrain investment across numerous sectors of the economy. The National Association of Manufacturers estimates that the revised standard threatens at least 474 announced manufacturing projects representing nearly $1 trillion in investment and more than 122,000 jobs.

The joint brief advances two related arguments. First, the Clean Air Act requires EPA to complete a thorough review before revising a NAAQS, whether the agency acts during the regular five-year review cycle or earlier. Second, the major questions doctrine reinforces that statutory conclusion: Congress did not clearly authorize EPA to bypass the prescribed review process when exercising authority with substantial economic and political consequences. The brief urges the Supreme Court to grant the petitions and decide whether EPA may revise a national air-quality standard without completing the review Congress required.