Clement was referring to Zinke's comment last week that nearly one-third of Interior's 70,000 employees are not loyal to him or President Donald Trump. "I got 30 percent of the crew that's not loyal to the flag," Zinke said, comparing Interior to a pirate ship.

Democratic lawmakers have called on Zinke to apologize, but he has given no indication he will do so.

In their letter Wednesday, the GOP lawmakers said federal officials should be "held to the highest ethical standard" in adhering to rules regarding transparency and responsible use of taxpayer dollars. That includes Zinke and former Interior secretaries Sally Jewell and Ken Salazar, the lawmakers said.

"When violations occur, the public deserves to know. When willful violations occur, there should be consequences," Bishop and Westerman said. At the same time, "when partisan opportunists conflate diligent conformance to scandal, no one wins," they added. "Let's get all facts on the table (and) ensure taxpayers are protected."

Zinke said last week he's taken three charter flights while in office, including a $12,375 late-night trip from Las Vegas to his home state of Montana in June. Zinke said no commercial flight was available when he planned to fly for a speech to Western governors.