A federal judge on Tuesday blocked Republican U.S. President Donald Trump from firing the Democratic chair of a U.S. agency that hears appeals by federal government employees when they are fired or disciplined.

U.S. District Judge Rudolph Contreras in Washington, D.C., ruled, opens new tab that the president could not remove Cathy Harris from her position at the Merit Systems Protection Board before her term expires without cause.

The judge, an appointee of Democratic former President Barack Obama, had on February 18 issued a temporary restraining order that required Harris to be reinstated as the board's chair while he considered whether to issue a longer-term injunction based on her claims that Trump illegally fired her earlier that month.

At a hearing on Monday, Justice Department attorney Jeremy Newman had urged Contreras not to extend his order reinstating Harris. Newman argued that a ruling for Harris would encroach on the president's broad authority to remove "principal officers" who are exercising executive power at federal agencies.

A lawyer for Harris, Nathaniel Zelinsky, at the hearing said the Trump administration was advancing "breathtaking" legal arguments.

Zelinsky told Contreras he was not "powerless" to block the Trump administration's action against Harris.

Federal workers who lose their jobs can bring a challenge before the merit board, an independent three-member panel, seeking to be reinstated. That role could put it in a central spot as Trump moves swiftly to shrink the federal government's workforce.

The board has proved to be a potential roadblock in the Trump administration's efforts to carry out mass firings of probationary workers, after having halted the firing of six such employees at the request of a watchdog agency whose leader Trump has also sought to fire.

While last week's decision to stay the six employees' firings for 45 days only applies to a handful of the thousands of probationary federal employees recently terminated, their lawyers said they hoped to expand the order to cover others.

Legal experts, though, have cautioned that many workers caught up in Trump's mass firings may be discouraged from pursuing legal action due to the lengthy and complicated administrative process before the merit board.

Harris was appointed to the merit board in 2022 by Trump's Democratic predecessor Joe Biden to serve a seven year term. Trump fired her on February 10 and named Henry Kerner, a Republican, as acting chair of the board.

Trump's removal of Harris had threatened to result in the board losing quorum and being unable to decide cases, as the term of its remaining Democrat, Raymond Limon, expired on Friday.

Trump also sought to fire Hampton Dellinger, the head of the Office of Special Counsel, which is responsible for protecting federal employees from being punished for whistle-blowing and other practices and had brought the case that halted the firing of the six employees to the merit board.

A federal judge on Saturday ruled that Trump's firing of Dellinger, a Biden appointee, was illegal, after having already temporarily blocked his firing.

The Trump administration is appealing and is expected to ask the U.S. Supreme Court to intervene, after it declined an earlier request to clear the way for Dellinger's removal, arguing it is unconstitutional to place limits on the president's authority to remove agency officials.