Southwest Airlines will soon require travelers who don't fit within the armrests of their seat to pay for an extra one in advance, part of a string of recent changes the carrier is making.

The new rule goes into effect Jan. 27, the same day Southwest starts assigning seats.

Currently, plus-size passengers can either pay for an extra seat in advance with the option of getting that money back later, or they can request a free extra seat at the airport. Under the carrier's new policy, a refund is still possible but no longer guaranteed.

In a statement Monday, Southwest said it is updating some of its policies as it prepares for assigned seating next year.

“To ensure space, we are communicating to Customers who have previously used the extra seat policy that they should purchase it at booking,” the statement said.

It marks the latest change at Southwest, which had long been known for letting its passengers pick their own seats after boarding the plane, and for letting their bags fly for free, which ended in May. Those perks were key to differentiating the budget carrier from its rivals.

Southwest says it will still refund a second ticket under its new policy for extra seating if the flight isn't fully booked at the time of departure, and if both of the passenger's tickets were purchased in the same booking class. The passenger also needs to request the refund within 90 days of the flight.

If a passenger who needs an extra seat doesn't purchase one ahead of time, they will be required to buy one at the airport, according to the new policy. If the flight is full, the passenger will be rebooked onto a new flight.

Jason Vaughn, an Orlando-based travel agent who posts theme park reviews and travel tips for plus-size people on social media and his website, Fat Travel Tested, said the change will likely impact travelers of all sizes. Southwest’s current policy helped create a more comfortable flying experience for plus-size travelers, he said, while also ensuring all passengers have adequate space in their seats.

“I think it’s going to make the flying experience worse for everybody,” he said of the new rule.

Vaughn described the change as yet another letdown for Southwest loyalists like himself, likening it to Cracker Barrel's recent logo change that has angered some of the restaurant's fans.

“They have no idea anymore who their customer is,” he said of the airline. "They have no identity left.”

The airline has struggled recently and is under pressure from activist investors to boost profits and revenue. It also said last year that it would charge customers extra for more legroom and offer red-eye flights.