Dr. Anthony Fauci on Monday said he thought the U.S. should consider instituting a mandate that would require domestic air travelers to be vaccinated against COVID-19.

During an appearance on MSNBC's "Morning Joe," Fauci — a White House medical adviser — declined to say whether he had briefed President Joe Biden on such a policy. However, he did say a vaccine requirement to board domestic flights is "reasonable to consider."

"There's requirements whether you want to get into college or a university, if you want to work in certain places, and if you make vaccinations a requirement that's another incentive to get more people vaccinated," Fauci said. "If you want to do that with domestic flights, I think that's something that should be considered."

Fauci's comments come as hundreds of flights across the country were delayed or canceled as airlines experienced worker shortages amid COVID-19 outbreaks.

The current spike in COVID-19 cases is largely being driven by the omicron variant — a highly contagious strain that now represents at least 73% of all new cases across the U.S.

"We're in a tough situation with omicron. It's not something to be taken lightly," Fauci said.

Fauci noted that data from South Africa — one of the first countries to experience an omicron surge — indicate that the new strain may not cause as serious cases of COVID-19 as other strains.

While it's unclear how the virus will behave in the U.S., Fauci noted that officials are considering lowering the time of isolation from a COVID-19 diagnosis from 10 days to seven days to prevent further worker shortages in essential industries.

"Certainly, with the health care workers, we're going to be doing it," Fauci said, noting that the administration will consider lowering the isolation period for workers in other industries deemed "essential."

In September, Fauci told theSkimm Podcast that he would support a vaccine mandate for air travel.

According to the Centers for Disease Control and Prevention, the U.S. saw its second-highest day of new infections last week, with nearly 300,000 new cases on Monday alone. The current seven-day average of new cases is about 175,000 a day, up from about 118,000 on Dec. 14. During that same period, deaths have remained fairly stagnant, rising from an average of 1,100 per day to 1,200 per day.

Several large companies based in Texas — including two of America's largest airliners — have said they plan to keep COVID-19 vaccine mandates for employees in place, siding with federal authorities in a showdown between the White House and the governor of Texas.

American Airlines, Southwest Airlines and IBM all said Tuesday that they would continue to require their workers to be vaccinated against COVID-19, even though Texas Gov. Greg Abbott signed an order on Monday banning private businesses from enforcing such mandates.

In a statement to The Dallas Morning News, Fort Worth-based American Airlines said that "we believe the federal vaccine mandate supersedes any conflicting state laws, and this does not change anything for American."

Dallas-based Southwest Airlines issued a similar statement to The Austin-American Statesman.

The company said they were choosing to comply with an order by the Department of Labor's Occupational Safety and Health Administration — which will require businesses with over 100 employees to ensure their workforce is fully vaccinated — because the White House order "supersedes any state mandate or law."

On Tuesday, Southwest CEO Gary Kelly told CNBC that he is opposed to vaccine mandates but that his company will still require the shots because he is required to by federal law.

"I've never been in favor of corporations imposing that kind of a mandate," Kelly said. "But the executive order from President Biden mandates that all federal employees and then all federal contractors, which covers all the major airlines, have to have a (vaccine) mandate (by Dec. 8)."

IBM told Bloomberg that it would keep in place a vaccine mandate for workers at its Texas office because the company has contracts with the federal government, meaning under Biden administration rules, it must require its employees to be vaccinated.

"IBM is a federal contractor and must comply with federal requirements, which direct employees of federal contractors to be fully vaccinated against Covid-19 by December 8th or obtain a medical or religious accommodation," a spokesperson for the company said. "We will continue to protect the health and safety of IBM employees and clients, and we will continue to follow federal requirements."

The resistance from high-profile employers could set up a legal battle, should the state of Texas choose to file a lawsuit.

According to The Associated Press, new cases of COVID-19 and hospitalizations linked to the virus have fallen in recent weeks. However, the state has seen more than 67,000 total coronavirus deaths since the start of the pandemic.

NEW YORK — Half of American workers are in favor of vaccine requirements at their workplaces at a time when such mandates are gaining traction now that the government has given full approval of Pfizer's COVID-19 vaccine.

The new poll from The Associated Press-NORC Center for Public Affairs Research shows that 47% of in-person workers are in favor. About a quarter of all workers — working both remote and in-person — are opposed to such mandates.

The poll found similar findings for sentiments on workplace mask mandates. Half of Americans working — including 59% of those working remote — are in favor of requiring masks at work, with about one-third opposed.

About 6 in 10 college graduates — people who are more likely to have jobs that require them to work from home — support both vaccine and mask mandates at their workplaces. That compares to about 40% of workers without college degrees.

Kati Perry/AP

The poll results come just days after the Food and Drug Administration granted full approval to Pfizer's COVID-19 vaccine — a move that could prompt more businesses and local governments to require vaccinations.

In recent days, the Pentagon has provided more information on their requirement that all military members be vaccinated; the city of Chicago has mandated that all city employees get a shot and Delta Airlines has introduced policies that penalize workers who do not choose to get vaccinated.