A federal judge strikes down the mask mandate on planes and public transit.

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

In her ruling, Federal District Judge Kathryn Kimball Mizelle said that the mandate “exceeds the C.D.C.’s statutory authority and violates the procedures required for agency rule making under the A.P.A.,” referring to the Administrative Procedure Act, which was written to make sure that the executive branch follows protocol when it wants to change policies and issue regulations.

The ruling by Judge Mizelle, an appointee of President Donald Trump, came in a lawsuit filed last year in Tampa by a group called the Health Freedom Defense Fund.

She declared the mandate unlawful and vacated it — apparently shutting it down for now. It was not immediately clear whether the Justice Department would appeal her order. If so, it could ask the judge or an appeals court to stay her order so that the C.D.C. could continue to enforce it while the matter undergoes further litigation.

Charlie Savage and Noah Weiland contributed reporting.