Treasury Secretary Steven T. Mnuchin took military aircraft on at least seven occasions without adequate justification, his department's inspector general said in a report.
The inspector general concluded that while Mnuchin broke no law, the White House failed to meet the "rigorous" preapproval process intended to justify the need to use expensive military aircraft.
Mnuchin has been criticized for requesting a military aircraft for a trip to Kentucky during which he viewed the solar eclipse and a trip to Europe for his honeymoon in August. He withdrew the request for the honeymoon trip, according to the report from the counsel to the Treasury inspector general, Rich Delmar.
In total, Mnuchin requested government aircraft for nine trips, one of which was withdrawn and one that is scheduled for later this month. The report, released Thursday, found that each trip was classified as a White House support mission.
In order to get that classification, the president must have directed the official to take the trip and the department must show that commercial airlines were either not available or cost effective or that there was an emergency need or national security concern requiring military planes. Those guidelines are based on a 2011 memo from then-White House Chief of Staff William Daley.
Delmar found that for the majority of the trips Mnuchin requested, it was "not explicit" that President Trump had ordered the travel, and the department did not provide a detailed analysis of the trip. Most of the requests included a similar line saying the planes were needed "due to scheduling, logistics and secure communications needs."
This "single boilerplate statement constituted the whole analysis and justification for designation and use of military aircraft," Delmar wrote.
The inspector general's review found "no violation of law in these requests and uses."
"What is of concern is a disconnect between the standard of proof called for in the Daley memo and the actual amount of proof provided by Treasury and accepted by the White House in justifying these trip requests," Delmar wrote.
He recommended the White House and government departments require greater detail, particularly about cost and security needs, for future travel requests.
"We appreciate the Inspector General's thorough review of the Treasury's travel requests, which identified no violation of law regulation or ethics requirements in connection with the Departments' requests," a Treasury spokesperson said. "The department followed the same approval procedures and provided the White House the same level of justification as in previous administrations, including the Obama administration."
"The Inspector General suggested certain enhancements to the longstanding approval process, which we intend to incorporate fully going forward," the statement said.
The Office of Management and Budget said in a memo last week it was reviewing guidance for the use of government aircraft and suggested that officials should be using government air travel only in exceptional situations.
The report comes amid reports that three other administration officials have used private or military aircraft for trips, including former Health and Human Services Secretary Tom Price, who reportedly spent more than $400,000 on private domestic travel. Price resigned last week after Trump expressed anger at his use of private charter flights.
Oct. 9, 9:30 a.m.: This article was updated with Treasury's response.