A U.S. Senate subcommittee is taking aim at airlines and their growing use of fees for things like early boarding and better seats.

Executives from United, Delta, American Spirit and Frontier airlines will testify Wednesday to defend billions of dollars in airline seating fees at a U.S. Senate subcommittee hearing.

Executives from American, United, Delta, Frontier and Spirit are set to testify before a Senate panel Wednesday about their seating fees.

Frontier Airlines made a major announcement on Tuesday that the low-cost carrier would be adding first-class style seating in 2025, along with a host of other benefits for frequent flyer members. However, it doesn't sound like the customer experience is going to be improved for the average budget traveler.

The CEO of Frontier Airlines is upset that the government accused his company of gouging customers for bag fees. In an interview with Reuters, Barry Biffle compared flyers who try not to pay for checked bags to thieves.