DALLAS, Texas: Southwest Airlines is tightening its rules for plus-size passengers, introducing a new requirement that travelers who need an additional seat must purchase it when booking rather than waiting until they reach the airport.

The policy change takes effect January 27, the same day the airline will introduce assigned seating, ending its long tradition of open boarding.

Currently, plus-size customers can either pay for an extra seat in advance with the option of requesting a refund later or ask for an extra seat at the airport at no cost. Under the new system, passengers will still be eligible for refunds, but only if the flight is not full at departure, both tickets were bought in the same booking class, and the request is filed within 90 days. Refunds are no longer guaranteed.

Southwest said in a statement that the update is part of a broader overhaul of policies tied to the transition to assigned seating. "To ensure space, we are communicating to customers who have previously used the extra seat policy that they should purchase it at booking," the airline said.

Passengers who don't purchase an additional seat ahead of time will be required to buy one at the airport. If the flight is sold out, they will be rebooked on another flight.

The change is Southwest's latest move. In May, the airline ended its "bags fly free" policy, another once-defining perk that set it apart from rivals. The airline has also announced plans to charge more for legroom and add red-eye flights.

Jason Vaughn, an Orlando-based travel agent who runs the Fat Travel Tested website, said the policy will affect all passengers, not just plus-size travelers. "I think it's going to make the flying experience worse for everybody," he said, adding that the current system offered comfort while ensuring adequate space for all.

He described the move as another blow to longtime loyalists, comparing it to brand changes at Cracker Barrel that angered some of the restaurant's customers. "They have no idea anymore who their customer is. They have no identity left," Vaughn said.

The airline has struggled with performance issues and faces pressure from activist investors to boost revenue and profits, prompting a wave of policy changes.

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