Checking a bag—already a pricey proposition—will cost more if travelers want to do it on certain high-traffic weekends. Peak pricing will apply during the second half of April, June 20 through Labor Day, Thanksgiving, and the second half of December, according to JetBlue’s site. 

A person flying within the U.S. on a basic fare would pay $35 to check a bag during a non-peak time, as long as they paid the fee at least 24 hours before their flight, according to the site. But if they were flying during Thanksgiving week and checked luggage two hours before the flight, it would run them $50 for the first bag and $70 for the second. Fees also differ based on the traveler’s destination, their JetBlue membership level, the ticket price, and the exact weight of the luggage. 

Airlines’ fees for checked bags, choosing seats, or changing flights—known in the industry as “ancillary revenue”—reached a record $118 billion globally last year, making up about 15% of companies’ profits, according to IdeaWorksCompany, a consultant on this type of revenue.

Major carriers including Alaska Airlines, American, Delta, and United have all hiked the price to check bags in recent weeks. 

JetBlue told Fortune it was raising prices because its own costs for fuel and wages had gone up “significantly.”

“While we don’t like increasing fees, we are making these adjustments to help get our company back to profitability and cover the increased costs. By adjusting fees for added services that only certain customers use, especially during periods of highest demand for limited space in the cargo hold, we can keep base fares as low as possible,” the company said in an email, adding that in-flight WiFi and TV would remain free. The company noted it had not been profitable since the COVID-19 pandemic began. 

While airlines’ costs have certainly increased, the decision to hike fees and not ticket prices benefits carriers, because it makes it hard for travelers to price-compare among airlines, consumer advocates say.

“You can’t go on to Expedia or Kayak or Google flights and do an apples-to-apples comparison of the fees of different airlines. That’s not by accident,” John Breyault, an aviation expert at the National Consumers League, previously told Fortune. He noted that raising fees, as opposed to ticket prices, also lets airlines save on taxes. 

And dynamic pricing—changing the price of a service based on the time of day or its popularity—remains widely hated among consumers. 

The latest company to learn this lesson the hard way is Wendy’s. The fast-food chain’s CEO told investors in February he planned to introduce dynamic pricing—only to walk back the promise the following day after mass consumer outrage. Ticketmaster’s dynamic pricing has gotten blowback for driving already expensive concert tickets into the tens of thousands of dollars. Ride-hailing services Uber and Lyft frequently come under fire for surge pricing at times of heavy demand—including after tragedies such as a mass shooting in the New York subway in 2022. 

Most consumers equate dynamic pricing with price gouging, and many would drop retailers who use the strategy, a survey from eMarketer found last year. 

JetBlue customers who booked flights before March 22 will be exempt from the dynamic pricing, the company said. JetBlue isn’t the only budget airline to use this tactic, though—EasyJet says that fees “vary depending on the route selected, flight and time of booking.” It’s possible others will follow; as Breyault previously said, one company introducing added fees to a service often prompts others to do the same, since it’s so profitable. 

“I see it as a contagion,” he told Fortune. “One company starts doing it and making money off ancillary revenue and suddenly everyone starts doing the same thing.”