In a rare bipartisan move, the leaders of the Senate Judiciary Committee sent a letter to President Trump seeking an explanation for why he fired 18 inspectors general, who serve as federal agency watchdogs.

Chairman Charles E. Grassley, Iowa Republican, and ranking member Richard J. Durbin, Illinois Democrat, say the president must give Congress a 30-day notice before dismissing an inspector general. The senators say they want more information on why the watchdogs were fired and the names of the federal officials who will act in their place.

“This is a matter of public and congressional accountability and ensuring the public’s confidence in the Inspector General community, a sentiment shared more broadly by other Members of Congress,” the senators wrote in the letter, sent Tuesday. “IGs are critical to rooting out waste, fraud, abuse and misconduct within the Executive Branch bureaucracy, which you have publicly made clear you are also intent on doing.” 

The White House didn’t respond to a request for comment. 

In the letter, Mr. Grassley and Mr. Durbin said Mr. Trump may have violated the law by failing to notify Congress within those 30 days.

“While IGs aren’t immune from committing acts requiring their removal, and they can be removed by the president, the law must be followed. The communication to Congress must contain more than just broad and vague statements; rather it must include sufficient facts and details to assure Congress and the public that the termination is due to real concerns about the Inspector General’s ability to carry out their mission,” the letter said.

The president axed the 18 inspectors general on Friday without notifying Congress. The IGs of the Departments of Defense, State, Transportation, Labor, Health and Human Services, Veterans Affairs, Housing and Urban Development, Interior, Energy, Commerce, Treasury and Agriculture were among those fired. Some of those terminated were appointed by Mr. Trump during his first term. 

“It’s a very common thing to do,” Mr. Trump told reporters on Air Force One Saturday. “I don’t know them, but some people thought that some were unfair or some were not doing their job. It’s a very standard thing to do.”

He said the fired IGs were “not my people,” even though some were among his appointments.