Washington CNN  — 

A group of Republican senators asked the White House not to fire Ambassador Gordon Sondland, a key impeachment witness, a source familiar with the situation confirmed to CNN on Saturday.

The source told CNN the group included Sens. Susan Collins of Maine, Thom Tillis of North Carolina, Ron Johnson of Wisconsin and Martha McSally of Arizona.

Republican senators were concerned it would look bad for Trump to fire Sondland, and told White House officials that Sondland should be allowed to leave on his own terms, according to the New York Times, which first reported the story on Saturday.

The senators also said it was unnecessary to fire Sondland since the diplomat was speaking with senior officials about leaving after the Senate impeachment trial, according to the Times.

Johnson’s office declined to comment to CNN. The three other senators’ representatives have not returned CNN’s request for comment.

The White House did not immediately return a request for comment.

Trump on Friday fired two key impeachment witnesses, dismissing Sondland and Lt. Col. Alexander Vindman, the top Ukraine expert at the National Security Council. An adviser to Trump said the firings of the major impeachment witnesses was meant to send a message that siding against the President will not be tolerated.

The firings come two days after the Senate voted to acquit Trump on two articles of impeachment in votes that were largely along party lines.

Sondland’s ties to the White House and Trump had deteriorated since his impeachment testimony. Sondland once had Trump effectively on speed-dial, or the presidential equivalent of it, but since his appearance before Congress he hadn’t spoken with Trump, according to a person familiar with the situation. He was also pulled from overseeing the Ukraine portfolio, which wasn’t directly related to his position as EU ambassador.

The two dismissals on Friday appear to be retribution for Vindman and Sondland’s explosive testimonies to the House impeachment probe late last year, both of which were done under subpoena. The duo gave some of the most damning testimony to House impeachment investigators during last fall’s public hearings and quickly became targets for Trump’s supporters, both inside and outside of government.

“Flushing out the pipes,” an adviser told CNN. “It was necessary.”

The story has been updated with additional developments Sunday.

CNN’s Kaitlan Collins, Kristen Holmes, Katelyn Polantz, Gloria Borger, Kevin Liptak, Jim Acosta and Devan Cole contributed to this report.