As Health Secretary Robert F. Kennedy Jr. began moving to reshape oversight of preventive health guidelines, the administration fired the two doctors leading the U.S. Preventive Services Task Force, according to letters described in a report by The New York Times and summarized by the Associated Press. The panel, long influential in what insurers cover for free, reviews evidence across a range of conditions and prevention tools and assigns letter grades based on how strong the science is behind particular services.

In letters dated May 11, Kennedy notified Dr. John Wong and Esa Davis—who chaired the task force—that their appointments were being terminated immediately, before the end of their multiyear terms, the Associated Press reported. The letters said the task force’s work had benefited from the leaders’ “leadership, contributions and expertise,” while also encouraging them to reapply, but they did not spell out specific reasons for the firings, AP said.

The timing of the personnel change also comes amid what the AP described as a prolonged effort by the Department of Health and Human Services to keep the task force from operating normally. The department had already largely sidelined the panel over the past year, including indefinitely postponing scheduled public meetings, which left some updates in limbo, according to AP.

The task force, first created in the 1980s, is made up of experts who scrutinize the latest evidence behind many disease-prevention approaches, including a wide range of screenings and preventive interventions. Its guidelines are accompanied by letter grades that reflect the strength of the scientific support; under the Affordable Care Act, many insurance plans must cover preventive services that receive an “A” or “B” grade without requiring a co-pay.

AP reported that Kennedy’s letters did not clarify why Wong and Davis were removed. Kennedy wrote that the change was part of efforts to improve HHS oversight, including a stated review of task force appointments aimed at providing “clarity, continuity and confidence,” AP said.

The Associated Press said that an HHS spokesman did not respond to questions about why the two were fired. The letters were first reported by The New York Times, AP reported, and AP’s account also noted that Kennedy previously told lawmakers last month that he was reforming the task force. In that earlier testimony, Kennedy described the panel as “lackadaisical” and said he wanted it to meet more frequently and provide “for the first time, transparency.”

Former task force chairman Dr. Michael Silverstein said the past year’s sidelining amounted to a kind of government intrusion into scientific decision-making that he had not experienced during his 10 years on the task force, AP reported. Silverstein said he had seen the task force’s ability to publish certain updates and recommendations curtailed, including that the panel was not allowed to publish its final update to the cervical cancer screening guideline or to take steps to update recommendations about maternal depression, according to AP.

Aaron Carroll of the nonpartisan health policy group AcademyHealth told AP that the task force has staggered terms so health secretaries can appoint new members on a regular basis and make changes without upending the entire structure. The administration’s decision to remove the task force’s two chair doctors, however, raised questions among advocates about whether changes would preserve the expert-driven process that produces the evidence-based grades that insurers rely on to determine cost-free coverage.