"The American people are entitled to know the true cost of Buttigieg and his entourage of staffers flying private to destinations that have readily available commercial options."

On Feb. 27, the DOT's inspector general announced it would investigate whether Buttigieg's office has complied with federal laws regarding executive travel on DOT aircraft for official trips. The probe was requested by Sen. Marco Rubio, R-Fla., in response to a Fox News Digital report in December that revealed Buttigieg had taken 18 trips on the FAA planes since January 2021.

Following the Dec. 12 report, Fox News Digital filed a FOIA request for detailed information and costs of all flights logged by FAA planes since early 2021. For months, the DOT FOIA office repeatedly delayed providing the requested information, citing various reasons including on one occasion a key employee being out of the office, until Feb. 27, hours after the inspector general investigation was announced.

The information showed that in addition to Buttigieg's 18 flights, his advisers and communications team logged another three flights. However, the FOIA office opted to leave costs associated with all the flights carrying Buttigieg and his advisers blank and ignored multiple attempts for clarification.

Like Sutherland, Michael Chamberlain, the director of another watchdog group Protect the Public's Trust, expressed concern at the agency's apparent attempt to hide information from the public.

"Sadly, reports of unnecessary secrecy and selective release of information are all too common when discussing the self-proclaimed most transparent administration in history," Chamberlain told Fox News Digital. "And it appears that the more high-profile the issue or event, the greater the efforts to hide the information the public deserves to know."

"Contrary to what some agencies appear to believe, saving powerful officials from disclosure or embarrassment is not a legitimate reason to keep the public in the dark," he continued.

"Considering the potential abuse of taxpayer funds at issue, a necessary first step toward restoring the public’s trust in its government is for the Department of Transportation to come clean as to exactly how many taxpayer dollars were used to fly Secretary Buttigieg around on non-commercial flights."

DOT spokesperson Kerry Arndt declined to comment but referenced a Washington Post report that the total cost of 18 flights with Buttigieg as a passenger amounted to "about $42,000." That estimate did not factor in Buttigieg's travels on a Coast Guard plane or the flights his close advisers, including Arndt, took on the FAA planes without him.

Meanwhile, the agency has charged other agencies significantly more for flights on the same planes. For example, the Federal Emergency Management Agency (FEMA) paid $327,478 to the FAA for eight trips, and a total of 27 flights, to the sites of natural disasters in 2021 and 2022.

In one instance, the FAA charged FEMA Administrator Deanne Criswell and other officials $51,139 for a roundtrip flight in June from Washington, D.C., to Montana where catastrophic flooding had occurred. In September, the FAA charged FEMA $69,028 for flights to and from Puerto Rico in the aftermath of Hurricane Fiona.

"Because FAA already budgets for the operation, maintenance, and leasing of the fleet for core missions, DOT officials’ use of an FAA plane incurs marginal operating costs," the FAA said in a statement to Fox News Digital.

Buttigieg's predecessor Elaine Chao, who led the DOT throughout the Trump administration, was criticized after it was revealed she used government-managed planes on seven occasions in 2017, costing taxpayers about $94,000. At the time, the agency released detailed cost information in response to a FOIA request from a watchdog organization.