Treasury Secretary Steve Mnuchin speaking at the 2017 Delivering Alpha conference in New York on Sept. 12, 2017.

Treasury Secretary Steven Mnuchin asked for a costly government plane to fly to his European honeymoon earlier this year.

The Treasury's Office of Inspector General is looking into the request, according to ABC News, which first reported the story. Operating such a jet can cost around $25,000 an hour, according to ABC.

Mnuchin considered using a military plane because he needs access to secure communications as part of his national security duties, a Treasury spokesperson told CNBC.

"Treasury withdrew its request after a secure communications option was identified during the Secretary's extended travel," the spokesperson said.

The department inspector general's office is already examining a trip Mnuchin and his wife, Scottish actress Louise Linton, made to Kentucky last month. Mnuchin spoke at an event with Senate Majority Leader Mitch McConnell and examined gold reserves at Fort Knox, but he and his wife also allegedly took time to watch the solar eclipse during the trip.

Linton posted a now notorious Instagram photo of her and Mnuchin getting off a government plane at the end of the trip. She called out the designer brands she was wearing, then responded to an Instagram user with a long-winded comment defending her use of the jet and Mnuchin's contributions to the country.

"Do you think the US govt paid for our honeymoon or personal travel?! Lololol," Linton wrote in part of the comment.

Before becoming Treasury secretary, Mnuchin made his personal fortune as a Goldman Sachs partner, financier and major Hollywood movie producer.