United and American may ban passengers who don't wear masks

American and United Airlines are stepping up their mask policy enforcement.

Both airlines announced on Monday that all passengers will be required to wear masks per existing rules, but now those who refuse will face real consequences.

Beginning June 16 at American and June 18 at United, any passenger who does not wear a mask while traveling could be flagged for each airline's list of restricted flyers, possibly causing them to be barred from flying with the carrier again.

United offered slightly more details in announcing its policy, saying that the travel prohibition would last for a period of time that will be determined by the company after a "comprehensive incident review."

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Both airlines have technically required passengers to wear masks onboard since May, but many U.S. carriers had reportedly advised crews not to be heavy-handed in enforcing the policy and risk an in-flight incident with a passenger that refused to comply.

Now, the companies seem ready to bring down the hammer on unmasked flyers.

“Every reputable heath institution says wearing a mask is one of the most effective things people can do to protect others from contracting COVID-19, especially in places like an aircraft where social distancing is a challenge," Toby Enqvist, United’s chief customer officer said in a statement. "Today’s announcement is an unmistakable signal that we’re prepared to take serious steps, if necessary, to protect our customers and crew.”

Read more: Airline unions say government is failing flyers by not implement coronavirus rules.

Both airlines will permit passengers to fly without a mask if they have a medical condition or disability that prevents them from wearing one. And all travelers can temporarily remove their masks to eat, drink or take medicine.

United also provided a few more details about exactly how the policy will be enforced. Passengers who refuse to wear a mask will be reminded by cabin crews of the airline's policy, and those who continue not to refuse to wear a mask could eventually be flagged for possible future travel restrictions.

"Any final decision or actions regarding a customer’s future flight benefits will not occur onboard but instead take place after the flight has reached its destination and the security team has investigated the incident," the airline said in a press release.

Related: Sanitizer with your Stroopwafel? Many airlines are now providing cleaning supplies to passengers.

The policy updates by American and United's policy updates coincided with a Monday announcement from the Airlines for America (A4A) trade group, which said many of its members were stepping up enforcement of their onboard mask policies.

According to A4A, members would all enforce their mask requirements more strenuously and increase efforts to notify passengers about the rules before they travel. A4A represents big U.S. carriers, including American, Delta, Southwest and United

Related: United Airlines to mortgage MileagePlus for coronavirus funds, anticipates no impact to members.

Among current efforts: some airlines now require customers to acknowledge mask policies during check-in along with onboard announcements about the rules.

“U.S. airlines are very serious about requiring face coverings on their flights. Carriers are stepping up enforcement of face coverings and implementing substantial consequences for those who do not comply with the rules,” A4A president and CEO Nicholas Calio said in a statement. “Face coverings are one of several public health measures recommended by the CDC as an important layer of protection for passengers and customer-facing employees.”

Related: DOT will distribute almost 100 million face masks across the transportation sector.

For its part Southwest has required passengers to wear masks onboard since May 1, and said it will continue to bar passengers without a mask from boarding.

TPG has reached out to Delta to see if there are any changes to their mask policy enforcement practices. This post will be updated as that information becomes available.

This story was originally published on June 15, 2020 and was updated to reflect the new policy at American Airlines.