How airlines are hiding the cost of travel

Now the government wants to help them do it. Here's how to protect yourself.

Illustration by Christopher Elliott

When Carolyn DiDonato booked her ticket from Trenton, N.J., to Fort Myers, Fla., she says she was hit with a hidden airline fee.

On the last screen, concealed behind a drop-down menu, Frontier Airlines revealed that she would have to pay a nonrefundable $23 carrier interface charge for buying her ticket online.

"It was …