President Trump’s late-night ouster of the State Department watchdog on Friday came at the behest of Secretary of State Mike Pompeo—who was reportedly under investigation by the watchdog, The New York Times reports. A White House official who spoke on the condition of anonymity told the Times that Pompeo had recommended the dismissal of Steve Linick, the State Department’s inspector general since 2013. Trump agreed with the recommendation and sent a letter to House Speaker Nancy Pelosi announcing his intention to fire Linick because he said he no longer had the “fullest confidence” in him.

Democratic lawmakers immediately sounded the alarm over the move, warning that it “may be an act of illegal retaliation.” Rep. Eliot Engel (D-NY), the chairman of the House Foreign Affairs Committee, said Linick had recently opened an investigation into Pompeo. Engel and the highest-ranking Democrat on the Senate Foreign Relations Committee, Sen. Bob Menendez, formally launched an investigation Saturday into Linick’s firing. At the time of his ouster, Linick was said to be looking into claims that Pompeo misused his power to have a political appointee carry out personal tasks for him and his wife.