WASHINGTON – New Trump administration rules that give millions of people a shorter timeframe to sign up for the Affordable Care Act’s health care coverage are facing a legal challenge from Democratic mayors around the country.

The rules, rolled out last month, reverse a Biden-era effort to expand access to the Affordable Care Act’s health insurance, commonly called “Obamacare” or the ACA. The previous Democratic administration expanded the enrollment window for the coverage, which led to record enrollment.

The Department of Health and Human Services rolled out a series of new restrictions for Obamacare late last month, just as Congress was weighing a major bill that will decrease enrollment in the health care program that Republican President Donald Trump has scorned for years. As many as 2 million people — nearly 10% — are expected to lose coverage from the health department’s new rules.

The mayors of Baltimore, Chicago and Columbus, Ohio sued the federal health department on Tuesday over the rules, saying they will result in more uninsured residents and overburden city services.

“Cloaked in the pretense of government efficiency and fraud prevention, the 2025 Rule creates numerous barriers to affordable insurance coverage, negating the purpose of the ACA to extend affordable health coverage to all Americans, and instead increasing the population of underinsured and uninsured Americans,” the filing alleges.

Two liberal advocacy groups — Doctors for America and Main Street Alliance — joined in on the complaint.

The federal health department announced a series of changes late last month to the ACA. It will shorten the enrollment period for the federal marketplace by a month, limiting it to Nov. 1 to Dec. 15 in 2026. Income verification checks will become more stringent and a $5 fee will be tacked on for some people who automatically re-enroll in a free plan.

Insurers will also be able to deny coverage to people who have not paid their premiums on past plans. The rules also bar roughly 100,000 immigrants who were brought to the U.S. as children from signing up for the coverage.

HHS said in a statement that the polices “are temporary measures to immediately tamp down on improper enrollments and the improper flow of federal funds.”

The mayors — all Democrats — argue that the polices were introduced without an adequate public comment period on the policies.

“This unlawful rule will force families off their health insurance and raise costs on millions of Americans. This does nothing to help people and instead harms Americans’ health and safety across our country,” said Skye Perryman, the president of Democracy Forward, which is representing the coalition of plaintiffs in the lawsuit.

The lawsuit does not challenge the Trump administration’s restriction on immigrants signing up for the coverage.

The Biden administration saw gains in Obamacare enrollment as a major success of the Democratic president’s term, noting that a record 24 million people signed up for the coverage, thanks to generous tax breaks offered through the 2022 Inflation Reduction Act.

But the program has been a target of Trump, who has said it is riddled with problems that make the coverage unaffordable for many without large subsidies. Enrollment in the program dipped during his first term in office.