WASHINGTON — A federal judge in Florida struck down the mask requirement on airplanes, trains, buses and other public transportation on Monday, less than a week after the Centers for Disease Control and Prevention had extended it through May 3.

The ruling left it up to individual airlines and local transit agencies to decide what to do, and by late Monday, the nation’s largest airlines had dropped their mask requirements for domestic flights. The Amtrak rail system said passengers and employees would no longer need to wear masks.

In a 59-page decision, Judge Kathryn Kimball Mizelle, who was appointed by President Donald J. Trump, voided the mandate — which also applies to airports, train stations and other transportation hubs — nationwide on several grounds, including that the agency had exceeded its legal authority under the Public Health Services Act of 1944. Because of the ruling, the masking order was not in effect for the time being, and the Transportation Security Administration would not enforce it, a Biden administration official said on Monday evening.