Attorney General Phil Weiser challenges unlawful rollback of landmark policy to fight greenhouse gas pollution

March 19, 2026 (DENVER) – Attorney General Phil Weiser today joined a coalition of states, counties and cities to challenge the U.S. Environmental Protection Agency’s unlawful attempt to rescind its 2009 endangerment finding – the agency’s fundamental determination that greenhouse gas pollution from motor vehicles drives climate change and endangers public health and welfare.

“We in Colorado know all too well the effects of climate change. With intensifying drought conditions, catastrophic wildfires, and the lowest statewide snowpack on record this year, our communities and economy face greater risks than ever before. The EPA has no legal or scientific basis to roll back the endangerment finding—a key national policy for fighting climate pollution. We are in court challenging this terrible decision so that we can have every tool available to protect our state and nation from the harmful impacts of climate change,” said Attorney General Weiser.

The 2009 endangerment finding was the direct result of the landmark 2007 U.S. Supreme Court decision in Massachusetts v. EPA, which confirmed that the federal Clean Air Act authorizes EPA to regulate greenhouse gas emissions that endanger public health and welfare. Based on years of rigorous scientific analysis and review, EPA in 2009 determined that emissions from motor vehicles contribute to air pollution that harms public health and the environment, and the agency then set federal standards to limit and significantly reduce greenhouse gas emissions from cars and trucks.

Now, almost two decades later, EPA has rushed a rulemaking process to rescind the endangerment finding and repeal all motor vehicles greenhouse gas standards, blatantly disregarding the law and science. EPA’s rescission is based on flawed interpretations of the law—previously rejected by the Supreme Court—that the agency lacks authority to regulate greenhouse gas emissions. The rescission also ignores decades of peer-reviewed scientific evidence confirming the reality and severity of climate change. By eliminating all existing and future federal vehicle greenhouse gas emission standards, the rule violates EPA’s legal obligations, fundamental principles of administrative law, and its mission to protect public health and welfare.

Today’s lawsuit is the latest action taken by Attorney General Weiser and the coalition in their ongoing effort to fight back against EPA’s unlawful rescission of the 2009 endangerment finding. In the fall of 2025, 23 attorneys general and seven counties and cities submitted two comment letters urging EPA to abandon the proposal, arguing that it would violate settled law and scientific consensus, as well as cause unprecedented disruption to the regulatory landscape with catastrophic consequences for residents, industries, natural resources, and public investments.

Co-led by the attorneys general of California, Connecticut, New York and Massachusetts, Attorney General Weiser is joined in filing this challenge by the attorneys general of Arizona, Delaware, Hawai‘i, Illinois, Maine, Maryland, Michigan, Minnesota, New Jersey, New Mexico, Nevada, North Carolina, Oregon, Rhode Island, Vermont, Virginia, Washington, Wisconsin, and the District of Columbia. In addition, this challenge is joined by Pennsylvania Governor Josh Shapiro; City of Boston, Mass.; City of Chicago, Ill.; City of Cleveland, Ohio; City of Columbus, Ohio; City and County of Denver, Colo.; City of Los Angeles, Calif.; City of New York, NY; City and County of San Francisco, Calif.; County of Santa Clara, Calif.; and Harris County, Tex.

Read the petition for review (PDF).

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Media Contact:
Lawrence Pacheco
Chief Communications Officer
(720) 508-6553 office
lawrence.pacheco@coag.gov