(CNN)Participants at a food supply roundtable convened by Vice President Mike Pence in Iowa on Friday removed their face masks before Pence arrived, according to video from the event posted online.

       The session at the West Des Moines headquarters of Hy-Vee grocery stores came hours after Pence's press secretary tested positive for coronavirus, delaying his flight to Iowa and prompting a scramble inside the White House to identify people who also could have been exposed.

       In the video, which was streamed by the Des Moines Register and first posted by The Intercept, executives from Mountaire Farms, Smithfield, Kroger and Tyson Foods remove their face coverings after an unidentified person emerged from backstage and motioned removing a mask.

       None of the companies represented immediately responded to a CNN request for comment.

       The identity of the person was not immediately clear but a source familiar with the event's planning said she was there on behalf of the administration.

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       A source familiar with the situation told CNN that the staffer went out and "politely informed everyone that because they were six feet apart that, if they'd like, they could remove their mask."

       "She didn't ask and she didn't tell" them to remove their masks, the source said, noting that CDC guidelines say masks are not necessary if it's possible to maintain six feet of social distancing.

       A few minutes later, Pence emerged to begin the roundtable, which focused on outbreaks at meat processing facilities and safety concerns at grocery stores.

       A White House official told CNN the vice president's advance staff "takes precautions to keep round table participants distanced at at least six feet -- meaning you don't need to wear a mask based on CDC guidance -- so to allow for them to not wear masks and have a more engaging dialogue."

       "Participants, who have their temp taken and are screened by physicians, are always more than welcome to do whatever they'd like," the official said.

       The White House has said that anyone who comes in close proximity to Pence or President Donald Trump is administered a coronavirus test, and people entering the White House undergo temperature screening.

       But mask wearing has been rare among senior White House staff -- a fact that's drawn scrutiny after two West Wing staffers tested positive for the virus last week.

       Pence himself drew criticism when he visited the Mayo Clinic in Minnesota without wearing a mask, despite the facility's rules that all visitors must wear one. Later, he said he should have worn a mask and did cover his face when visiting a GE plant a few days later.

       Trump, however, has not been photographed wearing a mask and has said he can't envision wearing one at the White House. While visiting a mask production facility in Arizona last week, he briefly wore one backstage, but people familiar with the matter said he seemed uncomfortable and was told by factory management that it wasn't necessary to wear one.

       Last month, the White House updated its recommendations on wearing masks, suggesting Americans cover their faces when social distancing is difficult.

       At the White House, masks have been an infrequent sight among staffers, who often take the President's lead in their messaging and behavior.

       Since Pence's staffer and a military valet who served the President in the Oval Office both tested positive, masks have been more visible, including on Secret Service personnel.

       Chief of staff Mark Meadows told reporters last week that people who serve the President would start wearing masks.

       Trump administration officials spent the weekend scrambling as they attempted to do contact tracing for Katie Miller, Pence's press secretary who tested positive for coronavirus last week.

       But they had not identified who Miller contracted the virus from as of Sunday, raising concerns inside the White House about how to contain the outbreak.

       Pence will not self-quarantine and plans to be at the White House Monday

       Iowa's Republican Gov. Kim Reynolds, who participated in Pence's roundtable on Friday and also visited the White House last week, announced Monday that she is following a modified quarantine protocol for coronavirus out of concern that she may have been exposed to the virus during her trip. Reynolds said she did not have direct contact with the Pence staffer, but says she will follow a modified quarantine out of an abundance of caution.

       Some aides expressed concern at how Monday would proceed without greater clarity on how the virus had originated and spread. One official said it wasn't certain which colleagues would stay home. Some officials who had extended contact with Miller announced they would self-quarantine, while others who had similar contact with her did not.

       In conversations this weekend, Trump has expressed concern that aides contracting the virus would undercut his message that the outbreak is waning and states should begin reopening, according to a person who spoke with him.

       Trump voiced frustration that two White House staffers tested positive for coronavirus and has asked why his valets weren't ordered to wear masks before this week, according to the person.

       Trump believes an economic rebound will only come when governors decide to lift restrictions and is concerned at any signs the virus is resurgent.

       At the same time, he's told people he doesn't want to be near anyone who hasn't been tested and has bristled when coming into contact with some people at the White House.

       Pence is not planning to enter self-quarantine and arrived at the White House on Monday morning without wearing a mask.

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