If some passengers wanted to get off a flight, the plane would have to abandon its place in the line waiting for takeoff, taxi back to the gate and wait while baggage handlers removed luggage, said David A. Castelveter, a spokesman for the Air Transport Association, the trade group for the major carriers.

Image JetBlue passengers waited for hours to leave Kennedy Airport for Cancun on Feb. 14, 2007. Credit... Lou Martins/Associated Press

At this time of year, the plane then may have to go through de-icing again, Mr. Castelveter said. As delays mounted, he added, there was a far higher chance that the crew would be unable to continue, given the limits on their working hours.

“There will be more cancellations than there are today,” he said.

Others in the industry also suggested that some passengers would face unnecessary delays as airlines adjusted their practices to steer clear of the penalties, which could amount to millions of dollars for a violation on a single flight.

But passenger advocates were ecstatic that airlines would have to pay more attention to human comfort.

Kate Hanni, who founded FlyersRights.org after she was stuck with her family for nine hours on a plane diverted from Dallas to Austin, called it “a Christmas miracle.”

The rule, which applies only to domestic flights, is set to go into force in four months.

Its effects will differ from airport to airport. Planes are sometimes held on the ground in fine weather at uncongested airports because of a problem at the destination airport, and in those cases, making an extra stop at the terminal to let passengers off may cost the airlines nothing unless travelers eventually have to take seats on other flights. Or the plane may be waiting on a ramp near the terminal.

In other cases, it could be more complicated, as planes may be far from the terminal, and the rule specifies that they arrive back at the gate within three hours, not that they turn around after three hours.