House Speaker Nancy Pelosi, D-Calif., on Wednesday imposed a mandatory mask policy for the floor of the House.
Pelosi first revealed the new rule during a call with senior Democrats shortly before announcing it in the House chamber, a source on the call told CNBC.
Members of Congress and congressional staff will be required to wear face masks the entire time they are in the chamber, except when they are recognized to speak, Pelosi said on the floor Wednesday evening.
Failing to do so will be considered a "serious breach of decorum," she added.
The new policy comes just hours after Texas Republican Rep. Louie Gohmert announced he had tested positive for the coronavirus.
Gohmert had reportedly tested positive before boarding Air Force One to travel to Texas with President Donald Trump. Gohmert said in a video posted to social media later Wednesday that he had tested positive in two different Covid-19 tests at the White House.
Pelosi, when asked about Gohmert's diagnosis earlier Wednesday, said, "I'm so sorry for him. But I'm also sorry my members are concerned because he has been showing up at meetings without a mask and making a thing of it. Hopefully now he will look after his health, and others."
Gohmert appears to be the 11th member of Congress to test positive, a list that had thus far included nine members of the House and one senator, Kentucky's Rand Paul.
Masks, like most other aspects of the coronavirus pandemic, have become heavily politicized. Republicans are significantly more likely than Democrats to say they never wear a mask when outside their homes, recent polling shows.
Trump himself has largely resisted wearing a mask, and has cast doubt on their utility as an effective tool to prevent the spread of the coronavirus.
But last week he appeared to strongly endorse the use of face masks, tweeting, "many people say that it is Patriotic to wear a face mask when you can't socially distance. There is nobody more Patriotic than me, your favorite President!"
Pelosi made clear in her remarks in the chamber Wednesday evening that members of Congress and their staff "will not be permitted to enter the hall of the House without wearing a mask." She said masks will be made available by the doors of the House floor for those who do not have them.
She added: "The chair would also like to remind members that the speaker has the authority to direct the sergeant at arms to remove a member from the floor as a matter of decorum."
-- CNBC's Christina Wilkie contributed to this report.