President Biden fired Social Security Commissioner Andrew Saul on Friday amid an ongoing dispute over his leadership of the independent agency responsible for administering retirement and disability benefits.

Saul was one of the few remaining federal appointees from former President Donald Trump’s administration. The White House said he was fired after refusing a request for his resignation. Deputy Social Security Commissioner David Black was also asked to resign and he complied.

The Washington Post was first to report Saul's dismissal. He questioned the legality of Biden's decision in an interview with the newspaper and said he plans to be at work on Monday.

"I consider myself the term-protected Commissioner of Social Security," Saul said.

The White House recited a list of grievances against him.

"Since taking office, Commissioner Saul has undermined and politicized Social Security disability benefits, terminated the agency’s telework policy that was utilized by up to 25 percent of the agency’s workforce, not repaired SSA’s relationships with relevant Federal employee unions including in the context of COVID-19 workplace safety planning, reduced due process protections for benefits appeals hearings, and taken other actions that run contrary to the mission of the agency and the President’s policy agenda," a White House official said in a statement.

Biden appointed Kilolo Kijakazi to serve as acting commissioner until he appoints a permanent replacement. She currently serves as Deputy Commissioner for Retirement and Disability Policy at the Social Security Administration.

Sen. Chuck Grassley, R-Iowa, slammed Biden’s decision to fire Saul. He noted that both Saul and Black were confirmed by a "wide, bipartisan margin" in 2019 and had years remaining on their terms.

"Their terms didn’t expire until 2025, and there was no reasonable justification for these removals. President Biden is overtly politicizing the SSA," Grassley said in a statement. "People don’t want their retirement and benefits politicized, they just want an agency that works. We had that under Commissioner Saul."

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Sen. Ron Wyden, D-Ore., chair of the Senate Finance Committee, expressed support for Biden’s decision.

"Every president should choose the personnel that will best carry out their vision for the country. To fulfill President Biden’s bold vision for improving and expanding Social Security, he needs his people in charge," Wyden said. "I will work closely with the president to confirm a new commissioner as swiftly as possible to lead this critical agency."

Fox News’ Jacqui Heinrich contributed to this report.