New Trump administration rules that give millions of people less time to sign up for the Affordable Care Act’s coverage, and bar some immigrants from buying the health care coverage, are facing a legal challenge from Democratic mayors.

A group of Democratic-led cities sued the Trump administration Tuesday over new changes to the Affordable Care Act that they say will undermine the sweeping health care law and result in nearly 2 million Americans losing health insurance.

With a focus on controlling spending and preventing alleged fraud, the Trump administration imposes sweeping changes to the healthcare system: shorter enrollment periods, exclusion of “Dreamers,” and limitations on essential benefits.