Treasury Secretary Steve Mnuchin and his wife Louise Linton arrive on the Marine One helicopter with President Donald Trump aboard the deck of the aircraft carrier USS Gerald R. Ford for its commissioning ceremony at Naval Station Norfolk in Norfolk, Va., July 22, 2017.

Treasury Secretary Steven Mnuchin is coming under pressure from progressive groups to stop working on tax reform amid questions about his use of government aircraft during travel with his wife.

Not One Penny, a coalition of advocacy organizations protesting tax cuts for the wealthy, launched a new campaign Friday dubbed "Dump Mnuchin." It involves ads urging Mnuchin to end his participation in the so-called Big Six of Republican lawmakers and White House officials working on tax reform. The group also plans protests and advertising in cities where President Donald Trump travels to tout the issue. Though the group is not calling on Mnuchin to step down, it said he should not be involved in writing U.S. tax policy — one of the primary responsibilities of his job.

"The person who is leading Trump's work to change tax laws should not be abusing taxpayers to fund his private vacations," said Nicole Gill, executive director of Tax March, one of the groups involved in the effort. "It's time that the tax-writing effort take a vacation from Secretary Mnuchin."

The Treasury Department's inspector general is looking into all of Mnuchin's requests for and travel on government aircraft — including his request to fly on a U.S. Air Force jet during his European honeymoon this summer, said Rich Delmar, counsel to the inspector general. ABC News first reported the inquiry.

Mnuchin said Thursday that his staff wanted to ensure he had a secure form of communication while he was on vacation. Mnuchin said he eventually rescinded the request.

"I didn't use a government plane on my honeymoon, and if I had I would have paid for it myself. #FakeNews," Mnuchin tweeted.

Mnuchin tweet

Trump addressed the controversy Thursday aboard Air Force One as he flew to meet with the victims of Hurricane Irma. Trump said he did not know much about the incident but called Mnuchin an "honorable man" and said he has "total confidence" in him.

"I've known him a long time," Trump said. "He is a very straight shooter."

Mnuchin has also come under fire for giving a speech in Kentucky with his wife on the day of the solar eclipse. The Treasury defended the trip, which was taken on a government jet, as work-related and said the couple reimbursed the government for Linton's seat.

His wife also sparked criticism over social media after lashing out at an Instagram follower who criticized her photo of the trip filled with hashtags of the clothing designers she wore for the event.