The Trump administration moved Wednesday to reimpose work requirements for Americans on welfare, revoking an Obama-era policy that had urged states to apply for waivers exempting the poor from having to show they were either getting job training or looking for work.

Requiring work was a key part of the 1996 welfare reform law enacted by a GOP-led Congress and signed by then-President Bill Clinton, and Mr. Trump’s move restores the law as written.

“The waiver option offered by the Obama administration is being replaced today by an expectation that work should always be encouraged as a condition for receiving welfare,” said Steven Wagner, the Health and Human Services Department’s acting assistant secretary for children and families.

The 2012 Obama policy didn’t outright gut the welfare law. Instead, it pushed states to consider applying for waivers that would let them still pay benefits to people even if they weren’t actively seeking work, job training or meeting other criteria.

The move proved to be ineffective.

Just one state, Ohio, applied for a waiver in 2015, which “inexplicably” sat in limbo under President Obama, HHS said. Ohio applied again three months ago.

HHS said Wednesday that it informed Ohio the waiver was being denied.

Welfare reform was one of the major accomplishments of the Republican revolution that swept the GOP to control of Congress in the 1994 elections. The goal was to reduce the rolls by enticing able-bodied people into the workforce, and then tailoring assistance for those unable to work.

Mr. Obama’s administration created the work waiver in response to the former president’s executive action urging agencies to reform federal programs to dole out money more efficiently.

The 2012 HHS policy was supposed to let states test other ways to deliver welfare benefits, saying that if they wanted to skip the work requirement they had to lay out other performance targets to meet.

At the time of the announcement, Mr. Obama was heatedly criticized for what Republicans said was an unlawful move. They said there was no provision in the 1996 law to grant waivers.

Republicans cheered Mr. Trump’s restoration of the law.

“Chairman Brady believes that work requirements are essential to providing Americans with real paths out of poverty and up the economic ladder,” said Shane McDonald, spokesperson for House Ways and Means Chairman Kevin Brady. “Today’s action by the Trump administration ties in seamlessly to the work that he and the committee are doing to deliver policy solutions that truly improve the lives of American families nationwide.”

The 1996 law required states to show that a significant percentage of their welfare rolls — officially known as Temporary Assistance for Needy Families (TANF) — spent time on “work activities,” which could include actual work, but also school or job training.

Ohio, in its waiver request, had asked to allow welfare recipients more time in job training or on a job search.

It was unclear why the Obama administration never acted on the waiver.

Ohio’s Department of Job and Family Services didn’t respond to a request for comment.