Which other states joined California in suing the Trump administration on environmental policies?

1. Who exactly joined California this time — a clear list that settles the immediate question

Contemporary coverage of the June 2025 complaint identifies a coalition of 10 states that joined California in suing the federal government over the revocation of Clean Air Act waivers and the rollback of electric-vehicle and heavy-duty truck mandates. The states most consistently named across those June 2025 accounts are Colorado, Delaware, Massachusetts, New Jersey, New Mexico, New York, Oregon, Rhode Island, Vermont and Washington, which together sought judicial relief to preserve California’s authority to set stricter vehicle-emission standards and mandates ^{[1] [2] [3] [4]}. The plaintiffs frame the dispute as a legal question about whether the Congressional Review Act and related federal resolutions lawfully can nullify waivers Congress and prior EPA practice treated as distinct under the Clean Air Act. The June 2025 filings therefore reflect a coordinated multi-state challenge focused on the administration’s specific June actions.

2. Why sources report different totals — multiple lawsuits and shifting coalitions

The divergent counts in available documents stem from different lawsuits filed at different times and shifting coalitions joining particular complaints. A June 2025 suit lists 10 co-plaintiff states ^{[1] [3]}, whereas earlier or separate legal challenges against previous Trump-era rollbacks involved larger groups: for example, a 2019 lawsuit listed 22 states and numerous cities joining California in opposing an earlier national rollback of vehicle standards ^{[5] [6]}. Some accounts of the June 2025 matter say nine attorneys general joined in specific filings while other reports aggregate multiple related suits and pro forma add-ons to report totals of 10 or more ^{[2] [7]}. Thus, apparent contradictions reflect distinct cases, timing differences and the legal strategy of naming particular jurisdictions in each complaint rather than simple reporting errors.

3. The legal core: Congressional Review Act versus Clean Air Act waivers

The central legal contention in the June 2025 litigation is whether the Trump administration lawfully used the Congressional Review Act (CRA) to nullify waivers that had permitted California to enforce stricter standards for light- and heavy-duty vehicles and advanced clean-vehicle mandates. Plaintiffs argue the waivers are not “rules” subject to CRA disapproval and that revocation upends statutory allocations of authority under the Clean Air Act; defendants argue the resolution is valid and Congress’s disapproval has effect ^{[1] [3]}. Legal analysts cited in the reporting point to prior opinions from congressional and GAO offices indicating waivers may not be CRA-rule subject to disapproval, a technical but decisive issue that courts will resolve ^[3]. The June 2025 pleas thus aim to preserve state-level standards and prevent what plaintiffs call an unlawful federal circumvention of environmental law.

4. Historical context matters — earlier suits produced different alliances and legal theories

The 2019 litigation and other past challenges to Trump-era environmental rollbacks involved broader coalitions—for example, a 2019 suit joining California with as many as 22 states and dozens of cities targeted earlier EPA and NHTSA actions and invoked the Administrative Procedure Act and NEPA in addition to statutory arguments about the Clean Air Act ^{[5] [6]}. Those cases challenged federal agencies’ substantive rulemakings and supporting analyses that underpinned national standard rollbacks. The June 2025 complaints instead focus tightly on CRA disapprovals and the revocation of post-2020 waiver approvals tied to EV and truck rules, producing smaller, mission-focused coalitions of states that either face direct industry impacts or have aligned climate-polices to protect.

5. How to reconcile the reporting and what to rely on for a definitive answer

To reconcile differing counts, rely on the specific complaint filings and contemporaneous press releases from state attorneys general offices for the particular case date: the June 2025 complaint lists the 10 states named above ^{[1] [4]}. Broader tallies—9, 10, or 22—are not mutually exclusive facts but reflect distinct legal actions: some reports list attorneys general who joined particular papers in a single suit, others aggregate multiple allied suits over time. For readers seeking definitive, case-level verification, consult the court docket and the state AG press statements tied to the June 2025 filings; those primary documents confirm which jurisdictions joined that specific complaint ^{[2] [3]}.

6. Bottom line — a precise, evidence-based answer to the user’s original question

The most accurate answer for the June 2025 lawsuit is that 10 other states joined California — Colorado, Delaware, Massachusetts, New Jersey, New Mexico, New York, Oregon, Rhode Island, Vermont and Washington — in challenging the Trump administration’s revocation of vehicle-waiver and EV-related rules ^{[1] [2] [3]}. Historical disputes with larger coalitions exist and explain conflicting counts in some sources; those earlier suits in 2019 involved up to 22 states and separate legal claims ^{[5] [6]}. The variation is a product of different cases, different legal strategies, and evolving state alliances, not simple factual inconsistency.