WASHINGTON — The Interior Department’s internal watchdog said Monday it is investigating Secretary Ryan Zinke’s use of charter flights, even as Zinke dismissed the controversy over his taxpayer-financed flights as “a little BS over travel.”

Zinke disclosed Friday that he had taken three charter flights since taking office in March, including a $12,375 late-night trip from Las Vegas to his home state of Montana in June.

A spokeswoman for Deputy Inspector General Mary Kendall said the inspector general’s office was investigating Zinke’s travel. Two Democratic members of Congress requested the investigation.

Zinke is one of several Cabinet members facing questions about their travel after health secretary Tom Price came under criticism for using costly chartered planes while on government business. Price resigned on Friday.

Zinke said Friday that “taxpayers absolutely have the right to know official travel costs,” but he dismissed criticism of his flights as “a little BS over travel.”

No commercial flight was available from Las Vegas at the time he planned to fly for a speech to Western governors the next day in Whitefish, Montana, Zinke said.

Zinke, a former Montana congressman, was in Las Vegas to speak to the Vegas Golden Knights, the city’s new National Hockey League team. The team’s owner, Bill Foley, contributed to Zinke’s congressional campaigns.

Zinke also traveled by private plane in Alaska in May and to the U.S. Virgin Islands in March. Zinke wants to expand energy production in Alaska, while the Interior Department oversees the U.S. Virgin Islands.

Zinke said he also went on a military flight with Agriculture Secretary Sonny Perdue to view wildfires in Montana in August.

All of his travel was approved in advance by Interior’s ethics officials “after extensive due diligence,” Zinke said, adding that he works hard to “make sure I am above the law and I follow the law.”

Zinke’s office did not provide the costs for his Alaska or Virgin Island trips, but it said in a statement that commercial flights were not available in either case.

Democratic Reps. Raul Grijalva of Arizona and Donald McEachin of Virginia requested the investigation. Grijalva is the senior Democrat on the House Natural Resources Committee, while McEachin is top Democrat on the panel’s subcommittee on oversight and investigations.

The Trump administration “tells us there’s no money for Medicare, Medicaid, public education or enforcing environmental standards, but there’s plenty for them taking twelve-thousand-dollar flights instead of sitting in coach,” Grijalva said.

The flap over private flights echoes a controversy over improper travel expenses submitted by Zinke when he was a Navy SEAL.

A 1999 report by the Navy faulted Zinke for improper travel expenses submitted for two flights to Montana, including one in which he reimbursed the Navy for $211. The other trip, from training in Washington state to his Whitefish home, did not require reimbursement.

Zinke told The Associated Press in 2014 that he “learned a valuable lesson that I still hold today, that you are always accountable for your actions.”

Zinke was a candidate for Congress at the time. He won the single seat representing Montana in the House that year and re-election in 2016 before being named Interior secretary.

Zinke said the travel disputes occurred because his commanding officer disagreed with his belief that Montana should be used for SEAL training.

Zinke’s office did not respond to requests for comment.

Sen. Maria Cantwell, D-Wash., said she welcomed the investigation, adding that if it concludes Zinke misused public funds, “he should promptly reimburse the taxpayers.”