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.

Blumenthal suggested that the fees are pure profit for the airlines because they do not need to create new seats each time the fee is charged or incur any other expenses at all wh

In a hearing that became heated, senators expressed frustration that executives wouldn’t reveal what determines the ancillary fees.