But at a roundtable discussion later during the visit, Pence removed his mask, as did other attendees, including Chao.

Pence was accompanied during the visit to the GM facility in Kokomo, Indiana, by Transportation Secretary Elaine Chao, Indiana Gov. Eric Holcomb, GM CEO Mary Barra and White House Trade advisor Peter Navarro — all of whom were also wearing masks.

U.S. Vice President Mike Pence and CEO of General Motors Mary Barra visit the General Motors Components Holding Plant that is manufacturing ventilators for use during the coronavirus disease (COVID-19) outbreak, in Kokomo, Indiana.

Pence, who once served as governor of Indiana, is leading the White House's coronavirus task force.

His tour of the recently reopened plant came two weeks after it began producing ventilators with Ventech Life Systems to deal with a shortage of the medical breathing assistance devices in the face of the coronavirus pandemic.

Brian Rothenberg, a spokesman for the United Auto Workers union, said that General Motors requires workers at the plant to wear surgical masks there except when they are eating lunch.

Pence has previously said that he does not need to wear a mask to prevent spreading an infection — despite federal health guidance to the contrary — because he is tested regularly for coronavirus, and has been shown to be negative for it.

Health experts have disputed that idea, saying the tests are not always accurate and that there is a risk that Pence could contract the coronavirus between tests and pass it on unwittingly to others.

The Mayo Clinic has said it told Pence's staff before he visited there Tuesday that masks were required for all visitors, staff and patients at its Rochester, Minnesota, facility because of the coronavirus outbreak.

But Pence's wife, Karen, on Thursday said during a Fox News interview that he only learned of the mask policy after he left the clinic Tuesday.

"As our medical experts have told us wearing a mask prevents you from spreading the disease and knowing that he doesn't have COVID-19, he didn't wear one," Karen Pence said on "Fox & Friends."

However, Voice of America reporter Steve Herman, in response to another journalist's tweet about Karen Pence's comment, tweeted Thursday that he and everyone else who had gone on the trip with Pence to Minnesota on Tuesday were "notified by the office of @VP the day before the trip that wearing of masks was required by the @MayoClinic and to prepare accordingly."

Tweet

Herman's tweet was echoed by Wall Street Journal reporter, Gordon Lubold, who tweeted: "... everyone in the entire Mayo Clinic had a mask on, everyone, and we were all told the day before we had to wear a mask if we entered the clinic."

The Washington Post reported Thursday evening that Herman, the White House bureau chief of government-funded VOA, had been told by Pence's staff that he had violated the off-the-record conditions of a planning memo that was sent to journalists before the trip to the Mayo Clinic.

The Post article said that the White House Correspondents' Association had told Herman that Pence's office had banned him from further travel with the vice president on Air Force Two. The Post said a spokesman in Pence's office later told VOA managers that "any punishment was still under discussion, pending an apology from Herman or VOA."

A spokeswoman for Pence did not immediately respond Thursday night to CNBC when asked about Herman.

The federal Centers for Disease Control and Prevention, in guidance issued in early April urging Americans to wear masks, says, "You could spread COVID-19 to others even if you do not feel sick."