Twenty-one states and four cities filed suit Thursday against the U.S. Environmental Protection Agency over the agency's September repeal of greenhouse gas emission limits for coal- and natural-gas-fired power plants.

The Democratic-led coalition, led by New York Attorney General Letitia James, filed its petition in the U.S. Court of Appeals for the District of Columbia. Plaintiffs include Pennsylvania's governor, the District of Columbia, New York City, Chicago, and the city and county of Denver.

The lawsuit targets the EPA's decision last month to revoke the Biden-era rule, which had set emissions standards for existing fossil-fuel power plants. The agency simultaneously proposed a separate rule that would prevent future administrations from regulating climate pollution from the same facilities.

EPA estimates the repeal will save the power industry more than $300 billion, according to the agency's announcement. EPA Assistant Administrator Aaron Szabo said in September the change will allow utilities to "make the best decision for the ratepayers based on cost and cost savings, instead of being required to shut down facilities."

What is the coalition arguing?

The plaintiffs contend the EPA unlawfully abandoned the pollution limits without evaluating reasonable alternatives or the public health costs of continued emissions. They describe the repeal as "gutting one of the country's most significant climate protections."

"Dismantling these protections is a betrayal of American families, and the stakes are too high to allow this administration to once again put profits over people," James said in a statement Thursday.

The 21 state plaintiffs are:

• Arizona
• California
• Colorado
• Connecticut
• Delaware
• Hawaii
• Illinois
• Maine
• Maryland
• Massachusetts
• Michigan
• Minnesota
• New Jersey
• New Mexico
• New York
• North Carolina
• Oregon
• Rhode Island
• Vermont
• Washington
• Wisconsin

The coalition has also notified the EPA of its intent to sue over the agency's failure to regulate emissions from many gas-fired power plants.

How is the EPA framing the rule change?

The EPA declined to comment on the pending litigation. In its September repeal announcement, the agency framed the move as cost relief for utilities and ratepayers. The agency earlier this year also revoked the underlying scientific finding — the endangerment finding — that had long served as the legal basis for U.S. greenhouse gas regulation.

A separate proposed rule, expected to be finalized in 2027, would lock in the policy reversal by preventing future administrations from re-regulating power plant emissions.

What is the next regulatory milestone?

The D.C. Circuit will docket the petition in the coming weeks. Briefing schedules have not been set. A ruling for the plaintiffs could force the EPA to reinstate the 2024 emissions standards for existing power plants.

Separately, the U.S. Supreme Court convenes Monday to hear Boulder, Colorado's climate damages suit against oil and gas companies. It marks the first day of the new term and the first time the justices will weigh municipal climate liability.

Analysts are watching both cases. A Supreme Court ruling in favor of Boulder could open a new front of climate-related litigation against fossil fuel producers, with billions in potential damages at stake.

The 2027 timeline on the EPA's separate "no backsliding" rulemaking is the next fixed deadline. Coalition attorneys have signaled they will challenge that rule once finalized, potentially consolidating the cases before the same appellate court.