The Trump administration issued guidance to states early Thursday that will allow them to compel people to work or prepare for jobs in order to receive Medicaid for the first time in the half-century history of this pillar of the nation’s social safety net.

The letter to state Medicaid directors opens the door for states to cut off Medicaid benefits to Americans unless they have a job, are in school, are a caregiver, volunteer or participate in other approved forms of “community engagement” — an idea that some states had broached over the past several years but that the Obama administration had consistently rebuffed.

The new policy comes as 10 states are already lined up, waiting for federal permission to impose work requirements on able-bodied adults in the program . Three other states are contemplating them. Health officials could approve the first waiver — probably for Kentucky — as soon as Friday, according to two people with knowledge of the process.

The guidance represents a fundamental and much-disputed recalibration of the compact between the government and poor Americans for whom Medicaid coverage provides a crucial pathway to health care.

The idea of conditioning government benefits on “work activities” was cemented into welfare more than two decades ago, when a system of unlimited cash assistance was replaced by the Temporary Assistance for Needy Families with its work requirements and time limits. The link between government help and work later was extended to anti-hunger efforts through the Supplemental Nutrition Assistance Program, as food stamps are now called.