Donald Trump's administration moved Thursday to let states require that able-bodied adults work in order to receive health care benefits through Medicaid, a pillar of the US social safety net.

The policy change would mark the first time the publicly funded program, which has insured the health needs of the poor and disabled since its creation in the 1960s, has been allowed to require for benefits.

The Health and Human Services Department outlined how could reshape the program in a directive.

"Medicaid needs to be more flexible so that states can best address the needs of this population," Seema Verma, administrator of the Center for Medicare and Medicaid Services, said in a statement.

"Our fundamental goal is to make a positive and lasting difference in the health and wellness of our beneficiaries, and today's announcement is a step in that direction."

The directive spells out who is excluded from the new work requirements, including children and the elderly, people with disabilities, pregnant women, and people being treated for opioid abuse.

But it makes suggestions for states as to what counts as work, including state work programs, job training, volunteering, or caring for a relative.

Several Republican lawmakers have supported work requirements as a condition for Medicaid coverage for able-bodied people, but such changes were not allowed until Thursday's memo.

At least 10 states, led by Republicans, were awaiting federal permission to enforce the new work rules, according to the Washington Post.

Nearly 20 percent of the population received Medicaid benefits in 2015, according to the US census.

Health insurance reforms initiated during Barack Obama's presidency raised the income cap for access to Medicaid, allowing millions of low-income earners to join the Medicaid rolls.

But many conservatives believe able-bodied adults should not be permitted to benefit from the coverage without either working, training or actively seeking a job.

The Obama administration opposed the demands by the states.

The shift under Trump could draw legal challenges from care, rights or seniors' groups.

House Democrat Eliot Engel called the decision "a cruel attempt to sabotage Americans' safety net."