Zinke disclosed last week that he has taken three charter flights, including a $12,375 late-night trip from Las Vegas to his home state of Montana.
A spokeswoman for the inspector general’s office, Nancy DiPaolo, says the office is investigating.
Zinke is one of several Cabinet members facing questions about travel after Tom Price resigned as health chief. Price came under criticism for using costly chartered planes while on government business.
Zinke said Friday that “taxpayers absolutely have the right to know official travel costs,” but he dismissed criticism of his flights as “a little BS over travel.”
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