An internal watchdog will conduct an audit of Transportation Secretary Pete Buttigieg’s use of Federal Aviation Administration (FAA) jets for official business, the Department of Transportation Office of Inspector General announced Monday.

The audit, prompted by a request from Republican Florida Sen. Marco Rubio, will analyze all trips taken by DOT secretaries since Jan. 31, 2017, according to the office’s memo. Rubio requested the audit to determine whether Buttigieg’s use of FAA planes complied with department guidelines after a Fox News report revealed Buttigieg flew on a private jet 18 times since taking office.

“The Office of Management and Budget’s (OMB) guidance to executive department heads allows executives to travel on Government aircraft but with restrictions,” the memo reads. “The guidance states that, to minimize cost and improve the management and use of Government aviation resources, Government aircraft shall be used only for official travel or on a space available basis, subject to certain policies and authorizations.”