Established by President Bill Clinton in 1995, the council can have up to 25 members who are appointed to four-year terms by the secretary of health and human services in consultation with the White House.

Gabriel Maldonado, the chief executive of TruEvolution, an advocacy group for lesbian, gay, bisexual and transgender people and an H.I.V. and AIDS services organization, who was among those dismissed, said federal officials could have removed him and his colleagues when Mr. Trump was inaugurated or at one of the two meetings the council held this year.

During those meetings, he said the council had voiced concerns over the Trump administration’s position on the Affordable Care Act, among other issues.

Six members announced their departure in June. Writing in Newsweek, one of the former members, Scott A. Schoettes, who is counsel and H.I.V. project director at Lambda Legal, said that “the Trump administration has no strategy to address the ongoing H.I.V./AIDS epidemic, seeks zero input from experts to formulate H.I.V. policy, and — most concerning — pushes legislation that will harm people living with H.I.V. and halt or reverse important gains made in the fight against this disease.”

Mr. Maldonado said he also found it strange that Mr. Trump issued an executive order in September continuing 32 advisory committees — including the council on H.I.V. and AIDS — whose operating authorities had been set to expire. That would have been an appropriate time to relieve the remaining members of their appointments, he said.

