How U.S. airlines are changing their mask rules.

Hours after a federal judge struck down a nationwide mask requirement on airplanes, trains, buses and other public transportation on Monday, the country’s largest airlines said they would stop requiring masks, ending a practice that had been in place for most carriers for nearly two years.

The airlines weighed in after a Biden administration official said the Transportation Security Administration would no longer enforce the mask requirement while the White House reviewed the decision and determined whether it would appeal the ruling.

Generally, the airlines said they would no longer require masks at airports and on flights within the United States, though several said they would still require them when flying into cities and countries where requirements were still in place. Some airports may continue to require masks, too.

Here’s what each of the major national airlines had to say.

American Airlines

In a statement, American said it had “prioritized the health and safety” of its employees and customers throughout the pandemic and supported federal measures to slow the spread of the coronavirus. While it will no longer require masks at airports and on flights within the United States, the airline said customers and employees could choose to wear them “at their own discretion.”

“We are deeply grateful to our team members for their enforcement of the mandate, and will share more information about this transition in the coming days,” American said.

Southwest Airlines

Southwest said in a statement that it was encouraging employees and customers “to make the best decision to support their personal well-being” about whether to wear a mask. The airline said safety on its flights would remain an “uncompromising priority,” pointing to the high-end air filtration on the planes that it and other carriers use.

Delta Air Lines

While Delta similarly announced that it would stop enforcing a mask requirement, the airline also asked for patience as the shift in policy was rolled out.

“Given the unexpected nature of this announcement, please be aware that customers, airline employees and federal agency employees, such as T.S.A., may be receiving this information at different times,” it said. “You may experience inconsistent enforcement during the next 24 hours as this news is more broadly communicated — remember to show understanding and patience with others who may not be aware enforcement is no longer required. Communications to customers and in-airport signage and announcements will be updated to share that masking is now optional — this may take a short period of time.”

United Airlines

United said that it would stop requiring masks on domestic flights, but that they would still be required on flights into countries where a mandate was still in place.

“While this means that our employees are no longer required to wear a mask — and no longer have to enforce a mask requirement for most of the flying public — they will be able to wear masks if they choose to do so, as the C.D.C. continues to strongly recommend wearing a mask on public transit,” the airline said.

Alaska Airlines

In a statement to customers, Alaska noted the significance of the moment and said it welcomed the opportunity to “see your smiling faces,” while acknowledging that some may still feel conflicted about the shift in policy.

“It has been a long 24 months with nearly constant change,” said Max Tidwell, the airline’s vice president of safety and security. “I could not be prouder of our frontline employees who have handled every pivot focusing on safety and the care we’re known for. We’re also thankful for our guests who remained considerate, patient and stood by us throughout every twist and turn.”

JetBlue Airways

JetBlue announced its shift in a short statement, noting that “mask wearing will now be optional,” though customers and flight crews are still “welcome” to wear masks in terminals and on the airline’s planes.

Spirit Airlines

Masks are now optional on Spirit, too, the airline said late Monday.

“We understand some guests may want to continue wearing face coverings on flights, and that’s perfectly fine under our optional policy,” it said. “For our guests traveling internationally, please remember to check country-specific airport requirements before traveling.”

Frontier Airlines

Like other airlines, Frontier said it would stop requiring masks on its planes, but cautioned that they might still be required at some airports and in some municipalities.

“Customers and team members should continue to abide by mask rules within any facility that may require it,” it said. “Per C.D.C. guidance, regardless of whether a mask mandate is in effect, individuals are encouraged to continue to wear masks in indoor settings.”