United Airlines hiked its checked bag fee by $10 on Thursday, becoming the second U.S. carrier in less than a week to raise the fee as the industry grapples with this year’s surge in fuel costs, airlines’ biggest expense after labor.

United’s new fee will be $45 to check a first bag on most domestic itineraries if the traveler pays ahead of time and $50 if they pay within 24 hours of their flight.

“United is raising first and second checked bag fees by $10 for customers traveling in the U.S., Mexico and Canada and Latin America beginning with tickets purchased Friday, April 3,” the carrier said.

United last raised checked bag fees in February 2024 and, like other carriers, is trying to cover the recent surge in jet fuel costs.

Fuel prices for Chicago, Houston, Los Angeles and New York averaged $4.88 a gallon on Thursday nearly double the price since the day before the U.S. and Israel attacked Iran on Feb.28, according to data from Argus published by industry group Airlines for America.

JetBlue Airways on Monday hiked its checked bag fees at least $4 per bag — and up to $9 per bag, depending on when a customer’s travel is booked — CNBC first reported.

Competitors often follow suit with such fee increases. There are loopholes, however. Airline credit cards often give customers a free checked bag when they’re on domestic itineraries in coach and it usually comes as a perk with elite frequent flyer status. Also, first-class seats generally include a free checked bag.

“United Chase credit card holders, MileagePlus Premier members, active military members and customers traveling in premium cabins can still check a bag for free, and customers in most markets will still enjoy a $5 discount if they prepay for their bags online 24 hours before their flight,” United said.

Higher fuel is showing up at gas stations and other sectors, too. Amazon is adding a 3.5% “fuel and logistics-related surcharge” to fees it collects from third-party sellers who use its fulfillment services, CNBC reported earlier Thursday.

— CNBC’s Annie Palmer contributed to this article.