CNN  — 

Republican Sen. Ted Cruz of Texas on Monday called Sen. Sherrod Brown “a complete ass” following a tense dispute over mask wearing on the Senate floor between the Ohio Democrat and Alaska Republican Sen. Dan Sullivan.

The dispute, captured in a video clip that has now gone viral, took place when Brown asked Sullivan to wear a mask while speaking as he presided over the Senate, a request that Sullivan refused to comply with.

Brown, who wore a mask as he spoke, said, “I’d start by asking the presiding officer to please wear a mask as he speaks.” Sullivan, who was not wearing a mask, responded tersely, “I don’t wear a mask when I’m speaking, like most senators, I don’t need your instruction.”

Cruz criticized Brown over the incident in a tweet on Monday, writing, “This is idiotic. @SherrodBrown is being a complete ass. He wears a mask to speak—when nobody is remotely near him—as an ostentatious sign of fake virtue.”

Sullivan addressed his heated exchange with Brown over masks Tuesday evening on Fox News, accusing the Democrat of seeking to “lecture” him.

“Some of these far-left senators like Senator Brown just can’t help themselves on their desire to want to lecture people on these kinds of issues, whether it’s lecturing other US senators or lecturing working families, and I think it’s a put-off,” Sullivan said. “People recognize the challenges – we’re going to get through these challenges – but to be lectured or preached to by senior officials is something that I think is not, not, I certainly didn’t appreciate.”

Brown told CNN’s Chris Cuomo on “Prime Time” later Tuesday that “Senator Cruz doesn’t have an intimate relationship with the truth in much of his public life.”

“The fact is that every time a senator stands up and speaks, there is a Senate stenographer about six feet away, and senators that don’t wear masks are putting them at risk,” he said. “I know that Ted Cruz doesn’t see the Senate stenographer because she is – it’s always a she in these cases – one of those essential workers that usually doesn’t get paid a lot of money and exposes themselves, those essential workers, to the public and then goes home anxious at night about potentially infecting their families.”

The series of events marks the latest flare-up on Capitol Hill over mask wearing and comes amid a deadly nationwide surge in coronavirus cases. A number of members of Congress have either tested positive or gone into quarantine following Covid-19 exposure in recent days.

While partisan finger-pointing is a frequent occurrence in Congress, it is highly unusual for a member to refer to a colleague by an obscenity. An obscure Senate rule, known as Senate Rule 19, prohibits a senator from impugning another while on the floor. Cruz’s remarks, however, came via Twitter and not while on the floor.

Cruz went on to say in his tweet that Sullivan was “over 50 feet away” from his fellow senator, adding that “last I checked 50 feet is more than 6 feet.”

It’s advisable, however, to wear masks indoors when other people are around even if 6 feet of distance can be maintained. Centers for Disease Control and Prevention guidance indicates that distancing is not a substitute for mask use when indoors. That’s because virus-laden particles can float in the air and accumulate in rooms. “Wear masks when less than 6 feet apart from other people or indoors,” the CDC website states in an explanation on steps to protect yourself at a social gathering.

Additionally, Cruz’s tweet was misleading, as Brown appeared to be referring to the staffers who were just a few feet away from Sullivan while he was maskless.

Brown made clear during a press call with reporters on Tuesday that he was expressing concern for Senate staff who must work on the floor, often nearby to where the presiding officer is seated.

“Mitch McConnell has called senators back where all the staff has to come down to the Senate floor and be exposed. They have no choice, they lose their jobs or they come to work, like most of America,” Brown said.

Of the confrontation with Sullivan, Brown said, “He was inches away from four people who had masks on, but couldn’t protect themselves from him.”

“I don’t care what they say to me. I care about public health. It’s clear that McConnell and some of my Senate colleagues, like Ted Cruz, care nothing about essential workers,” Brown said.

As the confrontation in the Senate continues to spark debate over mask wearing on Capitol Hill, Republican Sen. Chuck Grassley of Iowa tweeted Tuesday that he had tested positive for Covid-19, after his office had announced that morning that he had been exposed to the virus and would immediately quarantine.

Grassley, who as president pro tempore is the most senior Republican in the chamber, is 87 years old, putting him at a vulnerable age for contracting the virus. The Iowa Republican spoke on the Senate floor on Monday and was seen at the Capitol speaking to reporters Monday afternoon.

“I’m feeling good + will keep up on my work for the ppl of Iowa from home,” he said in his tweet.

Brown tweeted after the incident Monday, “I asked my Republican colleagues to stop endangering all the Senate workers - and simply wear a mask when presiding over the Senate.”

In his comments directed at Sullivan on the Senate floor, the Ohio Democrat pointed out that there are “people below him,” as he speaks.

He went on to say, “there clearly isn’t much interest in this body in public health.”

Since the pandemic has begun, there have been many occasions during which senators do not appear to be adequately socially distant on the Senate floor, especially during votes.

A CNN review of hours of footage from September 29 through October 1 showed senators often crowding one another – face-to-face and shoulder-to-shoulder – and carrying on extended conversations in the chamber.

This story has been updated with additional developments Tuesday.

CNN’s Ali Main, Caroline Kelly and Kristin Wilson contributed to this report.