This had nothing to do with convenience, Mnuchin told Politico Live. This was purely a national security issue.

ABC News reported that the honeymoon trip as well as the couples use of a military jet to travel to Louisville and Ft. Knox, Kentucky, last month were also under investigation. That trip coincided with the solar eclipse, which reached near totality in that area.

Mnuchin is not the only Trump official under fire for exorbitant travel costs. Tom Price, the head of the Health and Human Services Department, has racked up an estimated $300,000 in private charter flight costs. Politico reports that Price has utilized private planes at least 24 times since his confirmation in February.

This is Secretary Price, getting outside of D.C., making sure he is connected with the real American people, HHS spokeswoman Charmaine Yoest said in a statement to The Washington Post . Wasting four hours in an airport and having the secretary cancel his event is not a good use of taxpayer money.

ABC News spoke to former officials of the treasury and transportation departments who said this type of government travel was exceedingly rare and typically on overseas business flights.