The inspector general for the Interior Department is looking into the mode of travel Secretary Ryan Zinke used to attend a meeting with the Vegas Golden Knights hockey team, CNN reported Thursday.

Reuters was first to report on Friday that the inspector general was looking into Zinke’s travel and CNN confirmed that two Democratic members of Congress requested that the IG include the hockey team meeting — which cost taxpayers $12,375 to attend — in its probe.

Reps. Raul Grijalva (D- AZ) and Donald McEachin (D-VA) sent a letter to the Interior Department’s inspector general on Monday claiming Zinke could have taken a commercial flight home from Las Vegas if he hadn’t met with the team. They said Zinke doesn’t seem to see an issue with the expensive travel.

“Despite receiving substantial negative press, and despite Department of Health and Human Service Secretary Tom Price’s recent resignation over his use of privately chartered flights, Secretary Zinke made clear he will continue to use them,” they wrote.

The Office of Special Counsel has also opened a Hatch Act investigation into Zinke’s meeting with hockey players this summer. Zinke reportedly gave an inspirational speech to the Golden Knights, a team owned by Bill Foley, who was a major donor to Zinke’s campaign when he was running for Congress in 2014, according to CNN.

An Interior Department spokesperson told CNN that the private jet was booked for the meeting with the Golden Knights after no other commercial forms of travel were available. The trip was approved by the department’s ethics office, the spokesperson said.

The probe into Zinke’s travel is the sixth known investigation into how cabinet members are traveling on the taxpayer’s dime.

Read the full letter below:

