A new rule by the Trump administration could make it even harder for millions of sick Americans to obtain or stay on Medicaid after work requirements start next year.

The work requirement was established last summer as part of Republicans’ major tax and domestic policy legislation, and requires poor adults without disabilities to prove they worked, volunteered or attended school at least 80 hours a month or lose their Medicaid eligibility. Congressional leaders have described it as an effort to reduce “waste, fraud and abuse” in the program.

At the time the law passed, the Congressional Budget Office estimated around five million people would become uninsured because of the work requirement, including many who were working but unable to handle the paperwork to prove it. Medicaid currently covers about 68 million Americans who are poor or disabled.

The law laid out a series of exceptions for vulnerable people, including a carveout for people who are “medically frail.”

But the law did not define that term clearly. Some experts had said it was a way to protect people whose health problems might worsen if they lost their health coverage, like those with cancer. In informal conversations with states in recent months, Medicaid officials had indicated they were embracing that approach.

But other experts recently urged the administration to view frailty as meaning too sick to work. That stricter interpretation was reflected in the final rule. It says people’s medical conditions must “significantly impair” their ability to meet the work requirement, language that is not in the statute itself.