The House Oversight Committee is currently investigating an Air Force crew’s pit stop at an international Trump resort on its way to the Middle East.

The pit stop in question occurred early this spring, and was described by military officials as highly unusual, Politico first reported.

An Air National Guard crew was on its way to deliver supplies to Kuwait when it stopped at President Donald Trump’s Turnberry resort in Scotland. During past similar trips, the C-17 crew would’ve stopped at U.S. military bases to refuel, such as Ramstein Air Base in Germany or Naval Station Rota in Spain. Fuel is generally also cheaper at military bases.

Instead, they refueled the plane at Prestwick Airport in Glasgow and stayed overnight at the Trump resort, a 30-minute drive away.

A senior Air Force official noted that crew would usually stay on a military base or a local hotel near the airport, making the trek to Turnberry even odder.

The House Oversight Committee was alerted to the stop this spring and sent a letter to Defense Secretary Patrick Shanahan requesting documents about military spending at Turnberry and Prestwick Airport. According to Oversight, the military has spent $11 million at the airport since October 2017.

“The Defense Department has not produced a single document in this investigation,” a senior Democratic aide on the committee said. “The committee will be forced to consider alternative steps if the Pentagon does not begin complying voluntarily in the coming days.”

House Oversight’s inquiry about the pit stop is part of a larger probe into whether the military is enriching the president’s personal properties.

The new details also come after House Oversight Chair Elijah Cummings sent letters to the White House, U.S. Secret Service, Trump Organization, acting White House Chief of Staff Mick Mulvaney, and Vice President Mike Pence’s Chief of Staff Marc Short requesting information about Pence’s recent stay at Trump’s Ireland resort. (RELATED: Cummings Opens Probe Into Pence’s Stay At Trump’s Ireland Resort)

Pence stayed at the resort in Doonberg, Ireland, which was 180 miles from his official business in Dublin.

Officials previously claimed that Trump properties are actually losing money — while the taxpayer saves money — because officials are staying at a discounted rate. After Trump’s $243,000 golf trip at Turnberry last July, a person familiar with the trip argued that the resort could’ve charged the full room rate to other guests if the president and Secret Service were not staying there.