Treasury Secretary Steven Mnuchin Steven Terner MnuchinLawmakers fear voter backlash over failure to reach COVID-19 relief deal United Airlines, unions call for six-month extension of government aid House Democrats plan to unveil bill next week to avert shutdown MORE's flights on military aircraft since March have cost $800,000, according to a report from the department's inspector general.

The secretary has made nine requests to use military aircraft since assuming his position in the administration earlier this year, including a request for when he travels to the Middle East this month.

However, the report did not find any instances in which Mnuchin used military aircraft for private travel.

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“What is of concern is a disconnect between the standard of proof called for” by the Office of Management and Budget “and the actual amount of proof provided by Treasury and accepted by the White House in justifying these trip requests,” the Treasury Department's inspector general wrote, according to The New York Times.

The department's inspector general was also looking into why he requested a government plane to take him and his wife Louise Linton on their European honeymoon.

The request was later withdrawn.

Mnuchin has faced intense scrutiny for his travel ever since Linton posted a photo on Instagram of her exiting a military plane in August with hashtags identifying the high-end designers she was wearing.

However, various other members of President Trump's Cabinet are in hot water for their travel spending as well.

Health and Human Services Secretary Tom Price Thomas (Tom) Edmunds PriceConspicuous by their absence from the Republican Convention Coronavirus Report: The Hill's Steve Clemons interviews Chris Christie Trump flails as audience dwindles and ratings plummet MORE submitted his resignation last Friday after it was revealed he racked up more than $400,000 in private jet flights.

Interior Secretary Ryan Zinke and Environmental Protection Agency Administrator Scott Pruitt are also under scrutiny for their use of private aircraft for government business, while Veterans Affairs Secretary David Shulkin spent nearly half his time on a recent international trip sightseeing and shopping with his wife, whose airfare was paid for by the government, The Washington Post reported.