Sen. Gary Peters Gary Charles PetersHillicon Valley: Subpoenas for Facebook, Google and Twitter on the cards | Wray rebuffs mail-in voting conspiracies | Reps. raise mass surveillance concerns Postmaster general says postal service can't return mail-sorting machines The Hill's Campaign Report: Trump faces backlash after not committing to peaceful transition of power MORE (D-Mich.) on Tuesday called on the Defense Department's internal watchdog to investigate whether the Air Force violated the law by staying at President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE's Turnberry resort in Scotland.

In a letter to the Pentagon's Office of Inspector General (OIG), Peters questioned whether the agency was trying to "curry favor" by spending money at the president's property.

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"Potentially unnecessary spending by the military at a for-profit business owned by the President raises serious concerns about conflicts of interest and threatens the trust that the American people have placed in our military," the Michigan senator wrote.

"Taxpayers should never be forced to wonder whether our Armed Forces are making decisions based on operational concerns or to curry favor by prioritizing the President’s business interests," he added.

A press release from Peters's office stated that the letter came in response to media reports concerning a C-17 military transport plane that landed in Scotland for refueling, which resulted in crew members staying at the Trump resort overnight.

In the release, Peters's office noted that "flights of this nature generally involve refueling stopovers at U.S. air bases in Germany or Spain, not airports near Trump resorts."

The New York Times reported that the Trump Organization has been engaged in a deal with the Scotland airport at which the crew landed to house U.S. military personnel who stop at the facility for refueling or other reasons.

“We provide a full handling service for customers and routinely arrange overnight accommodation for visiting aircrew when requested,” the Glasgow Prestwick Airport said in a statement Monday.

“We use over a dozen local hotels, including Trump Turnberry, which accounts for a small percentage of the total hotel bookings we make,” the airport added.