House Speaker Nancy Pelosi said anyone who breaks the new rule by not wearing a face mask could be removed from the house.
She took the decision after Louie Gohmert, a Texas Republican frequently spotted around the Capitol without a face mask after being tested positive on Wednesday.
He was expected to travel that day with US President Donald Trump.
House Speaker Pelosi, a California Democrat, said on the House floor on Wednesday evening that members would be granted permission to remove their masks when addressing the chamber.
“The chair expects all members and staff to adhere to this requirement as a sign of respect for the health, safety, and wellbeing of others present in the chamber and surrounding areas,” she said.
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Mrs Pelosi said she would view “failure to wear a mask as a serious breach of decorum”, warning the House Sergeant at Arms could remove anyone who did not wear a mask.
According to GovTrack.us 10 members of Congress, three Democrats and seven Republicans have confirmed they tested positive, or were diagnosed with COVID-19.
Mr Gohmert, 66, discovered he was positive when he was routinely tested under White House travel protocol because he had been due to fly with President Trump to Texas on Wednesday.
The eighth-term lawmaker came back to his office to tell his staff in person of the positive result. He wore a mask during the meeting, as stated by the US media.
He also gave an interview in which he considered whether his mask was to blame for infecting him.
“I can’t help but wonder if by keeping a mask on and keeping it in place, I might have put some germs – some virus – on to the mask and breathed it in,” he told Texas station KETK.
He was one of a contingent of around two dozen Republicans frequently spotted on the House floor without masks.
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On Tuesday, Mr Gohmert oftenly removed his mask during a nearly five-hour hearing with Attorney General William Barr.
A photo on Twitter shows the two men in proximity, none of them were wearing masks. According to the Department of Justice, Mr Barr will be tested for coronavirus as a result of the interaction.
Despite mixed messages early in the pandemic, public health experts now agree that wearing face coverings greatly suppresses the spread of coronavirus, and is vital to controlling the infection’s spread.
