Travel documents released to Politico through a Freedom of Information Act request show Interior Secretary Ryan Zinke spent more than $53,000 on three government helicopters over the summer, including one trip that culminated with a horseback ride with the vice president.

Zinke, Montana’s former representative in the U.S. House, is already being investigated for his use of taxpayer-funded travel to attend both political and personal events while serving as the Secretary of Interior.

Now, the top Democrat in the U.S. Senate Energy and Natural Resources Committee is urging the Inspector General to add Zinke’s helicopter rides, funded by the taxpayers, to its ongoing investigation.

“I’m calling (the) Inspector General to add Secretary Zinke’s use of taxpayer-funded helicopter rides to the ongoing investigation into his use of taxpayer-funded private jets,” Cantwell tweeted on Friday. “If he misused public funds, he should write the treasury a check for the full amount and apologize.”

Among the expenses reported by Politico, Zinke spent $8,000 on a helicopter to fly to an emergency management exercise in West Virginia. Zinke reportedly ordered the helicopter because his schedule didn’t allow him time to make the two-hour drive from Washington, D.C.

He was allegedly held up in Washington to attend the swearing-in ceremony for Rep. Greg Gianforte, R-Montana.

“The swearing-in of the congressman is absolutely an official event, as is emergency management training,” Interior Department spokeswoman Heather Swift told Politico. “Shame on you for not respecting the office of a member of Congress.”

Another trip saw Zinke order a helicopter to fly to Yorktown, Virginia, in July. While there, he toured a war battlefield and attended a roundtable hosted by the boating industry. According to Politico, he then ordered a helicopter back to Washington, D.C., in order to make a horseback ride with Vice President Mike Pence.

Zinke’s use of taxpayer-funded travel first surfaced in September after Politico reported that the Secretary had taken two charter flights to two U.S. Virgin Islands earlier this year, as well as trip from Las Vegas to Kalispell, not far from his home in Whitefish.

Zinke was in Las Vegas to give a motivational speech to the city’s new NHL hockey team, according to the Washington Post. His charter flight to Montana cost upwards of $12,000, though a commercial flight on Allegiant could be had for $300.

“As with previous Interior secretaries, the secretary traveled on charter flights when there were no commercial options available,” Swift said at the time.

Two years ago, Zinke was forced to acknowledge that he improperly billed the government for travel to Montana as a member of the U.S. Navy. In that case, he repaid $211 for one of the trips and called the oversight a “glitch.”