The Trump administration is facing rare bipartisan pushback for firing the director of the Centers for Disease Control and Prevention (CDC), amid turmoil at the US’ top infectious disease agency that prompted dozens of staff to walk out of its headquarters in protest on Thursday.

The White House has said Susan Monarez, who was confirmed as director of the Centers for Disease Control and Prevention just a month ago, was fired as she was “not aligned with the president’s agenda” – only for Monarez to refuse to depart. The official’s lawyers have said that, as a Senate-confirmed appointee, only Donald Trump himself can remove her.

Monarez was reportedly fired by Robert F Kennedy Jr, the US health secretary, for refusing to remove agency officials and committing to restricting proven vaccines.

Kennedy, who previously founded an anti-vaccine group, has long spread misinformation about immunizations and this week placed new restrictions on who can get Covid vaccines.

This stance, along with concerns about budget cuts and political interference to the work of the CDC, prompted the resignation of four top agency leaders. On Thursday, dozens of CDC staff walked out of their Atlanta headquarters in support of Monarez and the other departed leaders.

The extraordinary turmoil at the CDC has provoked bipartisan alarm in Congress, earning the Trump administration a rare rebuke from normally slavishly loyal Republicans.

“She’s been on the job for only three weeks and I am very concerned and alarmed by this removal,” Susan Collins, the Republican senator from Maine, said of Monarez. Collins said there was “no basis” to remove the CDC director.

Bill Cassidy, another Republican senator who chairs the senate health committee, said that an upcoming meeting of the Department of Health and Human Services committee that advises on vaccine use should be postponed due to the attacks upon the CDC.

“If the meeting proceeds, any recommendations made should be rejected as lacking legitimacy given the seriousness of the allegations and the current turmoil in CDC leadership,” Cassidy said, adding that “serious allegations” have been made about the lack of scientific process in vaccine recommendations.

Bernie Sanders, the independent senator, said that people of all political persuasions should be alarmed by the attempt to restrict access to vaccines, which he called “one of the greatest public health achievements of the 20th century”.

“We are witnessing a full-blown war on science, on public health, and on truth itself,” Sanders said. “In just six months, Secretary Kennedy has dismantled the vaccine review process, narrowed access to life-saving Covid vaccines and filled scientific advisory boards with conspiracy theorists and ideologues.”

The Trump administration shows no sign of backing down, however. In a press briefing on Thursday, Karoline Leavitt, the White House press secretary, criticized one of the departing CDC officials for using the term “pregnant people” in his resignation letter.

“I understand there were a few other individuals who resigned after the firing of Ms Monarez,” she said. “One of those individuals wrote in his departure statement that he identifies pregnant women as pregnant people, so that’s not someone we want in this administration anyway.”

The official, Demetre Daskalakis, resigned from his position as director of the National Center for Immunization and Respiratory Diseases at the CDC on Wednesday, accusing the administration of using the agency to “generate policies and materials that do not reflect scientific reality and are designed to hurt rather than to improve the public’s health”.

Daskalakis responded to Leavitt’s remarks in an interview on CNN. “I find it outrageous that this administration is trying to erase transgender people,” he said.

“I very specifically used the term pregnant people, and very specifically added my pronouns at the end of my resignation letter to make the point that I am defying this terrible strategy at trying to erase people and not allowing them to express their identities.

“So I accept the note from the press secretary and I counter that with: I don’t care.”