A Senate subcommittee on Tuesday criticized U.S. airlines large and small over fees they charge to select seats on flights.

Between 2018 and 2023 American, delta, Unitedspirit and Border According to the Senate Permanent Subcommittee on Investigations report, seat fees generated $12.4 billion, including for seats with extra legroom and those in “preferred” locations closer to the front of the plane or for window or aisle seats .

Last year, United’s revenue from seat fees totaled $1.3 billion, the first time since at least 2018 that the category exceeded revenue from checked baggage fees, the report said.

While most major U.S. airlines have eliminated change fees for standard economy tickets, they have added fees for selecting more popular or spacious seats on board. Airlines are also looking to offer more premium seats on board to increase revenue.

Eliminating so-called junk fees has been a priority for the Biden administration. Sen. Richard Blumenthal, D-Conn., the subcommittee chairman, said airline executives have been asked to testify about the practice at a Dec. 4 hearing titled “The Sky’s the Limit – New Revelations on Airline Fees.”

Airlines for America, a trade group representing the largest U.S. airlines, said air travel has become more affordable and customers can choose what they want to pay on board.

“The report shows that the subcommittee clearly failed to understand the value that the highly competitive U.S. aviation industry brings to customers and employees. Rather, the report merely serves as another discussion point for leisure travel,” the group said.

The report also criticized low-cost airlines Spirit and Frontier, saying they paid gate agents $26 million between 2022 and 2023 to “catch passengers who allegedly do not adhere to airline baggage policies, which these passengers often do.” forcing them to pay a baggage fee or miss their flight.”

Spirit said in a statement that “our products and pricing are transparent, our airport policies ensure guests are treated fairly and equally, and we comply with all tax laws and regulations.”

Frontier said the commissions for gate agents are “simply intended to incentivize our team members to ensure compliance with bag size requirements so that all customers are treated equally and fairly, including the majority who follow the rules.”