According to Washington watchdog group Citizens for Responsibility and Ethics in Washington (CREW), Mnuchin has frequently opted for using military aircraft for his travel instead of taking commercial planes, which would come at a much lower cost to the taxpayer.

In a new report, CREW detailed findings obtained through a Freedom of Information Act (FOIA) request. Between the spring and fall of 2017, Mnuchin reportedly took eight trips on military planes, totaling close to $1 million.

Existing law dictates that government aircrafts are to be used only for “official purposes,” and when there is “no commercial airline or aircraft…reasonably available,” reports CREW. The reports do not show that the trips in question received “White House Mission” designation, meaning they were made for official purposes. In addition, CREW contends that commercial planes were in fact “reasonably available” for several of these trips, and significantly less expensive.

The report goes on to allege that Mnuchin has “abused” his “easy access to military and other non-commercial aircraft for both business travel and what, upon closer inspection, appears to sometimes include personal travel.” Nevertheless, CREW conceded that several of Mnuchin’s predecessors had similarly used military aircraft for international travel. Where Mnuchin differed, however, was his apparent unwillingness to use commercial planes for domestic travel, the cost of which has totaled close to $200,000 to date.

A number of Trump administration officials have been scrutinized for their use of government funds in recent months. Ben Carson reportedly canceled a $31,000 furniture order earlier this month and Scott Pruitt reportedly spent $25,000 on a soundproof booth and publicly defended his first-class travel. Health Secretary Tom Price resigned in September after his costly travel was revealed.

Tony Sayegh, Treasury’s assistant secretary for public affairs, said in a statement that CREW’s report contains “falsehoods and mischaracterizations.”

“Even CREW concedes that the Secretary’s travel requests ‘bear a remarkable similarity’ to the requests submitted by secretaries in the Obama Administration, using the same approval process and level of justification. The documents CREW cites are the same documents that were examined by Treasury’s Inspector General in his review of Treasury’s travel, in which he identified no violation of law, regulation, or ethics requirements,” Sayegh said.

This story has been updated to reflect Sayegh’s statement.