New regulations from the Transportation Department require airlines to include all mandatory taxes and fees in advertised fares.
Until now, the department has allowed airlines and travel agencies to list government-imposed fees separately. Those fees can add 20 percent or more to a ticket's price.
The advertising rule will go into effect January 26.
Southwest Airlines, Allegiant Air and Spirit Airlines have filed appeals to have the rule overturned, arguing that it violates commercial free speech rights.