Supreme Court Declines to Weaken Citizen Enforcement Under Clean Air and Water Acts

June 30, 2025 – In a win for environmental advocates, the U.S. Supreme Court has denied review in two cases that could have significantly narrowed the scope of citizen suit enforcement under the Clean Air Act (CAA) and Clean Water Act (CWA).

Citizen Enforcement Lives Another Day

In its June 30 order list, the Court declined to hear ExxonMobil Corp. v. Environment Texas Citizen Lobby and Port of Tacoma v. Puget Soundkeeper Alliance, preserving lower court rulings that upheld private enforcement against alleged polluters.

In the ExxonMobil case, the Fifth Circuit affirmed a nearly $15 million civil penalty related to years of excess air emissions from Exxon’s Baytown refinery. The ruling relied on the CAA’s citizen suit provisions and the longstanding Laidlaw precedent, which permits private plaintiffs to sue violators even when penalties are paid to the government. Exxon’s petition had asked the Court to revisit Laidlaw, arguing that plaintiffs lacked standing because they could not receive direct monetary relief.

CWA Decision Backs State-Law Enforcement

The second petition came from the Port of Tacoma, which challenged a Ninth Circuit ruling that allowed environmental plaintiffs to enforce state-derived stormwater discharge standards under the CWA’s citizen suit provisions.

At issue was Washington’s Industrial Stormwater General Permit (ISGP), which imposed broader requirements than the federal standard. The Ninth Circuit upheld citizen enforcement of the permit’s state-law provisions, even where federal law might not require the same level of regulation.

Industry groups warned that the ruling created a circuit split with the Second Circuit’s 1993 Atlantic States Legal Foundation decision, which limited citizen enforcement to federally mandated permit conditions. The Solicitor General’s office filed an amicus brief supporting review, but the Court declined to take the case.

What This Means for Industry

For now, citizen groups retain broad tools to hold companies accountable for alleged violations of federal and state environmental requirements. The Supreme Court’s denial of certiorari signals a reluctance to revisit foundational doctrines supporting citizen standing and enforcement.

This outcome reinforces the need for facilities—especially those operating under complex CAA or NPDES permits—to closely monitor compliance not only with federal baselines but also with more stringent state-issued conditions. Citizen suit risk remains high, particularly in jurisdictions with active environmental watchdog groups and state programs that go beyond federal minimums.