• The leader of a flight attendants union on Tuesday encouraged airline passengers to wear a mask on flights if they're feeling sick.
• "This is not about extending this mask policy. It's more about how we're recognizing that we're looking out for each other," union leader Sara Nelson told CNBC.
• A federal judge on Monday struck down the Biden administration's national Covid mask mandate for public transportation.

The leader of a flight attendants union on Tuesday encouraged airline passengers to wear a mask on flights if they're feeling sick, telling CNBC she believes it's an act of "common courtesy."

The comments come one day after a federal judge in Florida struck down the Biden administration's Covid face-covering mandate for public transportation, including airplanes. The Transportation Security Administration said it will stop enforcing the pandemic policy, and the major U.S. airlines said they'd stop requiring masks, too.

In an interview on "Squawk Box," Association of Flight Attendants-CWA President Sara Nelson said she agrees with co-host Andrew Ross Sorkin, who said he thinks regardless of federal rules, people should wear a mask on public transportation if they have Covid or any other illness.

"I think if there's anything we've learned from this [pandemic], it has to be about common courtesy," Nelson said, while noting the union had adopted a neutral position on whether the mask mandate should remain because its membership was divided. The union represents nearly 50,000 flight attendants at 17 airlines, according to its website.

Nelson said that flight crews had masks on hand even before the Covid pandemic and would sometimes ask a passenger who is coughing repeatedly to put one on. "This is not about extending this mask policy. It's more about how we're recognizing that we're looking out for each other and not bringing our own problems or viruses to other people knowingly."

Before Monday's court decision, the national face-covering requirement was supposed to be in effect through May 3. The Biden administration had extended it numerous times dating back to last year, including just last week.

The Justice Department has yet to indicate whether it will be appeal the ruling from U.S. District Judge Kathryn Kimball Mizelle, who was appointed by former President Donald Trump in 2020.

"There's absolutely a sigh of relief from flight crews," Nelson said. "But there's also people who are really concerned — people who are immunocompromised, people who are taking care of kids who are under the age of 5 at home and haven't had access to the vaccine yet."

Masks had become a contentious issue on airplanes, causing a spike in disruptive passengers. Last year, cases related to people not wearing masks on flights accounted for more than 70% of the nearly 6,000 reports of unruly passenger behavior recorded by Federal Aviation Administration. Flight attendants had expressed serious concerns about their own safety in trying to enforce the requirement.

It's unclear how passengers and flight crew will approach masks in the near term while Mizelle's ruling remains unchallenged. The Centers for Disease Control and Prevention continues to recommend people wear masks during the pandemic.

CNBC's Sorkin sought to gain an understanding of how people are thinking about the issue in a Twitter poll. The vast majority of the initial 7,200 respondents to Sorkin's unscientific poll say they will wear a mask "while knowingly sick."

Nelson expressed disappointment that people who know they are sick would get on a plane without taking extra precautions such as wearing a mask.

"I'm a 25-year flight attendant. Every flight attendant knows that when you start out flying, you have to get your air legs underneath you and one of those things means you're going to get all of the viruses and you're going to an incredible immune system," Nelson said.

"The idea that people would say, 'I'm going to go on an airplane sick,' is pretty offensive to me," she continued. "That's my workplace. You're bringing that, and you have a greater risk that I'm going to be subject to your germs if you knowingly do that. I'm just talking about common courtesy here."