Donald Trump ordered the government to enforce a decades-old law that requires Americans who bring migrants into the country to take financial responsibility if they claim welfare benefits, the president’s latest attempt to curb U.S. immigration.

In a memo signed Wednesday, Trump directed his administration to spend the next 90 days developing rules for U.S. citizens to reimburse the government for each dollar of means-tested federal aid provided to immigrants they’re sponsoring. That means Americans who seek to bring family members to the U.S. could be obligated to pay the government back if the immigrants use programs such as food stamps, Medicaid, or the federal Children’s Health Insurance Program.

“Financial sponsors who pledge to financially support the sponsored alien in the event the alien applies for or receives public benefits will be expected to fulfill their commitment under law,” Trump said in the memo, which was released by the White House today.

Trump also ordered his administration to determine within 180 days which individuals could lose their ability to sponsor migrants based on delinquency.

The move relies on language in welfare-reform legislation signed by Democratic President Bill Clinton in 1996. The law was never fully implemented, and it’s not clear how it would work in practice.

Championed by Trump adviser Stephen Miller, the affidavit requirement largely appears to be an effort to deter Americans from sponsoring foreign family members to live in the U.S. Trump has repeatedly criticized what he calls “chain migration,” and has called for the U.S. to adopt a system in which educated and skilled immigrants would be favored for admission.

But the administration’s plans to enforce the requirement aren’t clear.

Federal public assistance programs are administered by different agencies, including Health and Human Services and the Department of Agriculture. Tracking benefits received by individual immigrants and billing the costs to their American sponsors would require coordination not only across the federal government but also with state and local jurisdictions that distribute the assistance. Further complicating the task, many immigration records are maintained only on paper.

Earlier this month, the president unveiled a plan to dramatically overhaul the composition of immigrants entering the country by limiting those eligible based on family connections. Applicants would largely be ranked based on their education, job prospects, and English proficiency, among other metrics. The White House also is trying to overhaul asylum policy to reduce the volume of migrants seeking refugee status at the southern border.

But the plan was essentially declared dead-on-arrival in Congress, in part because it doesn’t address protections for immigrants brought to the U.S. illegally as children — a provision that Democrats and some Republicans have called essential.

Trump has also outraged congressional Democrats by declaring a national emergency at the southern border in order to redirect money from the Pentagon to construction of his promised wall.