Over ten years ago, Environment Texas Citizen Lobby and Sierra Club filed suit against ExxonMobil on behalf of their members who live, work, and recreate in close proximity to one of Exxon’s largest petrochemical plants in the country. Alleging that their members suffer from a wide variety of air pollution-related injuries and invoking what is known as a “citizen-suit” provision of the Clean Air Act, these groups cited thousands of violations of the Act and sought to impose penalties on Exxon to prevent it from continuing to flout federal law. The case eventually went to trial, and the district court concluded, among other things, that the environmental groups had standing to assert their claims and that Exxon was liable for violating the Clean Air Act. Consistent with the Clean Air Act’s remedy provisions, the court ordered Exxon to pay civil penalties.

After three rounds of appeals related to various issues, Exxon petitioned for rehearing, challenging standing and the district court’s penalty calculation but not the fact that it had committed thousands of violations of the Clean Air Act. In February 2023, the United States Court of Appeals for the Fifth Circuit agreed to hear the case en banc, and CAC filed an amicus brief in support of the environmental groups.

Our brief urged the court to decline Exxon’s invitation to impose heightened standing requirements on citizen suits and reject its argument that such lawsuits infringe on the separation of powers. As we explained, neither history nor Supreme Court precedent is on Exxon’s side.

First, our brief focused on the deeply rooted history of citizen suits. We discussed how the citizen suit’s historical predecessor, the qui tam action, evolved from its emergence in thirteenth-century English common law into a creature of statute. By the time of the Founding, statutory qui tam actions were well established, and early state legislatures and the first Congresses passed countless laws authorizing qui tam prosecutions or containing “informer” provisions designed to incentivize private citizens to aid the government in ensuring that laws protecting the public welfare were obeyed. Despite all this, there is no Founding-era evidence of anyone questioning these suits on the grounds that they either infringed Article II or violated separation of powers principles more broadly. This is so even though relators in qui tam actions suffer no injury of their own (unlike citizen-suit plaintiffs), but acquire standing by stepping into the shoes of the government.

Second, our brief explained that the Supreme Court’s recent decision in TransUnion LLC v. Ramirez provides no justification for adopting stricter standing requirements for citizen suits generally nor any new guidance for this case specifically. As we explained, TransUnion addressed the types of harms that constitute concrete injuries for purposes of Article III standing and Congress’s power to create statutory injuries, but it did not call into question those statutes like the Clean Air Act which simply give private citizens a cause of action to sue when they suffer a separate and distinct injury. Accordingly, TransUnion’s discussion of the risk of infringement on Article II when a plaintiff fails to establish a concrete injury is simply inapplicable to this case—here there is no question that plaintiffs’ physical injuries are sufficiently concrete. In fact, we demonstrated that reading TransUnion as limiting citizen suits in the way proposed by Exxon would risk infringing on the separation of powers in a different way: allowing courts to nullify Congress’s express choice to authorize such suits.

In sum, our brief argued that citizen suits are part of a long tradition of legislative authorization of private enforcement of statutes intended to protect the public welfare. These laws were never questioned on separation-of-powers grounds at the Founding, and TransUnion supplies no reason for this Court to question them now, centuries later.

In December 2024, the en banc Fifth Circuit issued its decision, affirming the district court’s judgment from March 2021, which had held that the plaintiffs had established traceability for 3,651 days of Exxon’s violations of the Clean Air Act. The one-paragraph per curiam opinion expressed concerns over the long waiting period endured by both parties prior to the judgment, stating that “justice delayed is justice denied.” Various separate opinions made clear that the per curiam opinion resulted from the en banc court’s inability to garner a majority for any other disposition.

Judge W. Eugene Davis, joined by six other judges, issued a concurrence agreeing with the per curiam opinion’s reasoning but maintaining that it would affirm the district court’s April 2017 judgment, which had held that the plaintiffs had established traceability for over 16,000 of Exxon’s days of violations of the Clean Air Act. Judge Davis wrote that there was “no doubt” that the plaintiffs’ injuries were sufficiently concrete to prove standing. Echoing our brief, the concurrence stated that citizen suits do not violate separation-of-powers principles. The concurrence also echoed our brief’s concern that adopting Exxon’s unprecedented heightened standing analysis for citizen suits would subvert congressional authority.