DOT said it uncovered the violations during a September 2011 investigation of Travelocity. The agency said the website listed prices for flights that did not include the fuel fees higher than flights that did in lowest to highest price rankings.
Customers were not notified of the extra charges they would have to pay until they selected an itinerary, which is prohibited by the DOT advertising rules, the DOT said.
A lawsuit against the advertising rules that was filed by a group of airlines that had previously been fined by DOT was dismissed by a Washington, D.C., appeals court this week.
The suit, filed by Southwest, Spirit and Allegiant airlines, had alleged that the rules created more stringent rules for the aviation industry than other businesses.
Other requirements in the DOT's "Passenger Bill of Rights" include requiring airlines to refund fees for checked luggage that is lost and fines for keeping passengers on grounded airplanes for delays that last more than three hours.