President Donald Trump said Wednesday that hes not happy about Health and Human Services Secretary Tom Price using charter planes for official travel, according to a pool report.

The president also told reporters that he is looking into the controversy, and said well see when asked if he would fire Price.

According to a series of reports by Politico, Price has taken at least two dozen trips on private planes since May, costing taxpayers more than $400,000. Those trips, which White House press secretary Sarah Huckabee Sanders said Monday were not White House-approved, are now under investigation by the HHS inspector general .

The House Oversight Committee is also set to begin a probe into Prices travel, as well as trips taken by other administration officials.

In a letter sent to 24 federal agencies on Wednesday, committee chair Rep. Trey Gowdy (R-S.C.) and ranking member Elijah Cummings (D-Md.) requested details on trips that non-career officials have taken using government aircraft or private planes since Trumps inauguration.

Under 5 U.S.C. 5733, official travel on the part of federal employees must be by the most expeditious means of transportation practicable and commensurate with the nature and purpose of the [employees] duties, and by no means should include personal use, reads the letter.

Read the full letter here.