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.