The Supreme Court ruled on June 20 that fuel industry groups have legal standing to challenge the Environmental Protection Agency’s waiver that allowed California to implement its Advanced Clean Cars I standards. 

While this case concerns light-duty electric vehicle mandates, it represents another instance of legal challenges aimed at California’s ability to set its own vehicle emissions standards — an authority that also underpins electric truck regulations.

The decision arrives amid broader efforts to roll back clean vehicle policies. Just days earlier, former President Trump signed Congressional resolutions revoking EPA waivers issued during the Biden Administration for Advanced Clean Cars II, the Advanced Clean Trucks (ACT) regulation, and the Heavy-Duty Low-NOx Omnibus Rule—key policies driving electrification in both light- and heavy-duty fleet sectors.

The legality of using the Congressional Review Act to revoke those waivers is now being challenged. California and 10 other states quickly filed a lawsuit opposing what they called “illegal resolutions targeting California’s clean vehicles program.”

Supreme Court Ruling Opens Door for Challenge

The case focused on California’s earlier electric vehicle mandate, Advanced Clean Cars I.

In Diamond Alternative Energy LLC v. EPA, Valero’s Diamond Alternative Energy and other fuel industry groups argued that the EPA exceeded its authority under the Clean Air Act by granting California a waiver to enforce the rules. They claimed this harmed their business by lowering demand for liquid fuels.

In a 7-2 decision, the Supreme Court overturned a lower court ruling that had dismissed the case for lack of legal standing. The justices ruled that the fuel companies have standing to challenge the waiver and sent the case back to the lower court for reconsideration.

“The government generally may not target a business or industry through stringent and allegedly unlawful regulation and then evade the resulting lawsuits by claiming that the targets of its regulation should be locked out of court as unaffected bystanders,” wrote Justice Brett Kavanaugh for the majority.

Justices Ketanji Brown Jackson and Sonia Sotomayor dissented. Jackson noted that the Clean Car I rules are set to expire soon and questioned the court’s decision to intervene at this stage.

Narrow Ruling, Bigger Implications for Zero-Emission Vehicle Policy

The case did not directly address California’s longstanding authority under the Clean Air Act or the merits of its Clean Car I standards. Those rules remain in full force and effect, according to the Environmental Defense Fund.

“The Supreme Court declined review of a question challenging the constitutionality of the Clean Air Act provision authorizing California’s standards,” the organization noted.

However, the ruling spurs renewed legal scrutiny of California’s regulatory authority — an issue that could influence the future of EV mandates like Advanced Clean Cars II and Advanced Clean Trucks, which many states use to speed up fleet electrification.

For fleet operators, the case adds to growing legal uncertainty around state-level zero-emission vehicle rules. While EV-related regulations remain intact, continued challenges could impact long-term planning for vehicle procurement, compliance, and sustainability targets.