Democrats in US Congress on Saturday launched an investigation into President Donald Trump’s move to oust the State Department’s internal watchdog, accusing the president of escalating his fight against any oversight of his administration, Reuters reported.

Trump announced the planned removal of Inspector General Steve Linick in a letter to House of Representatives Speaker Nancy Pelosi late Friday night.

The top Democrats on the House and Senate Foreign Relations Committees questioned the timing and motivation of what they called an “unprecedented removal.”

“We unalterably oppose the politically-motivated firing of inspectors general and the President’s gutting of these critical positions,” House panel chairman Eliot Engel and Senator Bob Menendez, the ranking Democrat on the Senate Foreign Relations panel, said in a statement announcing the probe.

The two Democrats said it was their understanding that Secretary of State Mike Pompeo personally recommended Linick’s firing because the inspector general “had opened an investigation into wrongdoing by Secretary Pompeo himself.”

Linick is the fourth inspector general fired by Trump since early April following the president’s February acquittal by the Republican-led Senate in an impeachment trial.