The Trump administration is facing pressure to protect the Federal Aviation Administration from further layoffs after hundreds of workers were fired over the weekend.
The job cuts were part of a government restructuring under Elon Musk, an adviser to President Trump who is heading a cost-cutting initiative.
Mr. Musk’s team has helped push through layoffs of thousands of workers across the government, including at the Transportation Department. But at the same time, the department’s secretary, Sean Duffy, has asked Mr. Musk, whose companies span the sectors of technology and transportation, to aid in addressing the agency’s aging air traffic control technology.
The firings come at a time when the F.A.A., the nation’s premier aviation safety agency, is dealing with several deadly plane crashes across the country, including a midair collision between an Army helicopter and American Airlines plane that killed 67 people on Jan. 27.
About 400 probationary workers — who were “hired less than a year ago” — were cut from the agency, according to Mr. Duffy, in a social media post on Monday responding to criticism from his Democratic predecessor, Pete Buttigieg.
“Zero air traffic controllers and critical safety personnel were let go,” Mr. Duffy wrote.
The Transportation Department added in a statement that the agency was continuing to hire and train air traffic controllers and aviation safety workers. However, union representatives say that some of the fired employees served in important support roles.
The layoffs included about 300 workers represented by the Professional Aviation Safety Specialists union. Afterward, Dave Spero, the union’s national president, and Senator Richard Blumenthal, Democrat of Connecticut, called for the Trump administration to halt additional work force reductions at the agency.
The notice of termination sent to employees said that they were being let go because “D.O.T. F.A.A. finds, that based on your performance you have not demonstrated that your further employment at the D.O.T. F.A.A. would be in the public interest,” according to an email an employee received.
Mr. Spero said he disagreed with the rationale for the firings. He said that although the laid-off workers did not include air traffic controllers and aviation safety inspectors, those who were let go were critical support and administrative staff who assisted safety personnel.
The workers who were dismissed included maintenance mechanics and aviation safety assistants, Mr. Spero said.
“They aren’t safety-of-flight people but the rest of us can’t do our jobs without them, and that’s the impact of losing these people,” he said.
Mr. Blumenthal sent a letter to Mr. Duffy on Wednesday calling for the firings to be reversed, saying they posed safety risks.
“A string of recent aviation incidents has shaken the public’s confidence in the safety of air travel and the trust placed in the agencies responsible for keeping our skies safe, the F.A.A. and Department of Transportation,” Mr. Blumenthal said in the letter.
In addition to the layoffs, anxiety grew in the aviation industry after employees from Mr. Musk’s aerospace company, SpaceX, visited the F.A.A.’s air-traffic command center in Warrenton, Va., on Monday as well as a facility that manages air traffic in and out of the nation’s capital.
Representatives for Mr. Musk’s team, the so-called Department of Government Efficiency, did not immediately respond to a request for comment.
Mr. Duffy said in a social-media post on Sunday that the visit would allow the SpaceX team members to see the system firsthand so they could better understand the technology challenges that air traffic controllers face.
“America deserves safe, state-of-the-art air travel, and President Trump has ordered that I deliver a new, world-class air traffic control system that will be the envy of the world,” Mr. Duffy wrote. “To do that, I need advice from the brightest minds in America.”