Hundreds of thousands of Americans who rely on the federal food stamp program will lose their benefits under a new Trump administration rule that will tighten work requirements for recipients.

The move by the administration is the latest in its attempt to scale back the social safety net for low-income Americans. It is the first of three proposed rules targeting the Supplemental Nutrition Assistance Program, known as Snap, to be finalized. The program feeds more than 36 million people.

The plan will limit states from exempting work-eligible adults from having to maintain steady employment in order to receive benefits.

The agriculture department estimates the change would save roughly $5.5bn over five years and cut benefits for roughly 688,000 Snap recipients. That’s down from its original estimate that 750,000 people would lose benefits.

Under current rules, work-eligible able-bodied adults without dependants and between the ages of 18 and 49 can currently receive only three months of Snap benefits in a three-year period if they don’t meet the 20-hour work requirement. But states with high unemployment rates or a demonstrable lack of sufficient jobs can waive those time limits.

The new rule imposes stricter criteria states must meet in order to issue waivers. Under the plan, states can only issue waivers if a city or county has an unemployment rate of 6% or higher. The waivers will be good for one year and will require the governor to support the request.

The final rule will go into effect in April.

The agriculture secretary, Sonny Perdue, said the rule will help move people “from welfare to work”.

Congressional Democrats and advocates for the poor were quick to condemn the administration’s actions.

Senator Debbie Stabenow said the plan will only serve to punish workers whose jobs are seasonal or unreliable.

“This administration is out of touch with families who are struggling to make ends meet by working seasonal jobs or part time jobs with unreliable hours,” said Stabenow, the top Democrat on the Senate committee on agriculture, nutrition and forestry.

Robert Greenstein, the president of the Center on Budget and Policy Priorities, said the rule would disproportionately affect minorities. He urged better job training and a higher minimum wage instead.

“Denying them basic food and nutrition is not the route that a fair and compassionate administration of either party should take,” he said in a statement.

Over the past year the agriculture department has proposed three significant changes to the food stamp program. In addition to restricting time limit waivers, the USDA has proposed eliminating broad-based categorical eligibility, a measure that allows recipients of certain non-cash public benefits to automatically qualify for food stamps, and changing how utility costs are factored into benefit calculations.

Brandon Lipps, the deputy under secretary for the US Department of Agriculture’s Food Nutrition and Consumer Services, did not say when the department will finalize the other two proposed rules.

The Urban Institute in a study released last month estimated that taken together, the three measures would affect roughly 2.2m households, and 3.7 million individual beneficiaries.

James D Weill, the president of the Food Research and Action Center, said the plan is “deeply flawed and ill-conceived“ and would lead to higher rates of hunger and poverty.

“The final rule would cause serious harm to individuals, communities and the nation while doing nothing to improve the health and employment of those impacted by the rule,” he said.