Rick Pazdur, the FDA’s top drug regulator, told staff Tuesday he submitted his resignation to the agency, an abrupt departure weeks after he was convinced by Commissioner Marty Makary to take the post to help bring stability to an agency reeling from months of upheaval, according to four people familiar with the decision granted anonymity to discuss the move.

The decision — which comes days after top vaccine regulator Vinay Prasad said the agency would ratchet up regulatory requirements for new vaccines — is almost certain to raise new questions about Makary’s leadership of the FDA.

Pazdur in recent weeks clashed with Makary over the Commissioner’s National Priority Voucher program, according to media reports.

That program — which aims to speed final review of drugs that address health priorities, pose a transformative innovative impact, address an unmet medical need, help onshoring efforts or increase affordability — was also criticized by Pazdur’s predecessor, George Tidmarsh. FDA experts have worried the involvement of political appointees in the process of choosing which firms receive a voucher could raise questions about the program’s integrity.

STAT first reported the news of Pazdur’s decision to retire. It is unclear if the decision is final — one person familiar with the decision said the longtime cancer drug regulator has 30 days to change his decision.

“We respect Dr. Pazdur’s decision to retire and honor his 26 years of distinguished service at the FDA,” an FDA spokesperson said in a statement. “As the founding director of the Oncology Center of Excellence, he leaves a legacy of cross-center regulatory innovation that strengthened the agency and advanced care for countless patients. His leadership, vision, and dedication will continue to shape the FDA for years to come.”

The White House and Pazdur did not immediately respond to requests for comment.

Pazdur, a 26-year agency veteran, initially rebuffed efforts by Makary to convince him to assume leadership of the FDA’s Center for Drug Evaluation and Research — but ultimately agreed to take the job after being assured he would be given autonomy in the role free from political influence and the ability to rehire staff.