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The federal mask requirement for planes and public transit was struck down on Monday by a federal judge in Florida. Within 24 hours, all major US airlines and the Amtrak rail system declared that they were no longer requiring masks for passengers or employees.

The White House said on Tuesday that it would appeal the ruling if the Centers for Disease Control and Prevention decided that there is a public health basis for trying to restore the mandate. The C.D.C. asked the Justice Department to proceed with an appeal.

What does this mean for travelers? The situation could change again soon.

No. All major U.S. carriers allow passengers and crew to wear a mask on flights.

New York's John F. Kennedy International and La Guardia airports are exceptions to the rule. It is possible that the requirements could change at each airport.

Depending on the country and the airline's rules, face coverings may still be required at some international destinations.

There are mask rules in different countries. Many nations, including China, Canada, France and Germany, still require travelers to wear masks on flights. It is up to the airline to set its own rules in Mexico and other parts of the Caribbean.

British Airways and Virgin Atlantic made masks optional on flights to the U.S. They used to require masks on many routes to the Caribbean.

Yes, indeed. Travelers over the age of 2 must show a negative coronaviruses test before boarding a plane. People who have tested positive in the past 90 days may travel with positive test results and a letter from a licensed health care provider or public health official saying that they have been cleared for travel.

There is no expiration date on this requirement. The C.D.C. requirement is financially damaging to the airlines and trade organizations that represent the hotel industry. The White House said there were no immediate plans to remove the rule.

It depends. Airlines don't seem to be giving special refunds for people in this situation. You may be out of luck if you booked a nonrefundable fare. Most airlines don't charge change fees on basic economy flights, so you may be able to get a credit or rebooking the flight.

A spokesman for Delta said on Wednesday that they hear situations out on a case-by-case basis.

Depending on the type of ticket, Southwest can give you a voucher or a refund.

American Airlines sent a standard policy that requires travelers to cancel their tickets within 24 hours.

Travelers are concerned about the sudden change of mask rules. Many people with diseases are grappling with what to do about upcoming travel plans. Ms. Speier knew that everyone on the plane would be wearing a mask.

I am angry that the airlines are doing it and that they are doing it suddenly, according to Ms. Speier, who writes a newsletter about living with a weakened immune system.

Carnival Cruise Line, Royal Caribbean and Norwegian are some of the major cruise lines that do not require mask-wearing. The voluntary sailing order of the C.D.C. does not require cruise passengers to wear masks onboard ships when 95 percent of crew and passengers over the age of 5 are fully vaccineed.

Following Monday's ruling on mask mandates for public transportation hubs, masks are no longer required to be worn in cruise terminals. Before disembarking from an international port, mask rules should be checked.

It depends. Since the federal transportation mandate no longer holds, public transit systems can set their own rules. In New York City and Portland, Ore., riders are required to wear masks, but not in Washington D.C. or Los Angeles. Passengers and employees will no longer need to wear masks on trains and stations. Adding to confusion, mask-wearing may be required in some train stations.

Drivers and riders in the United States no longer have to wear masks in taxis or on ride-sharing services. Local regulations can supersede the policies. In New York City, masks are still required in taxis.