Spirit Airlines was fined $50,000, the U.S. Department of Transportation announced today, for deceptive advertising that did not include fees and taxes upfront in ads on billboards and posters, as well as advertising tweets by the airline.

DOT rules require all price advertisements for air travel to list the full price to be paid by the consumer, including all carrier-imposed surcharges.

Starting in June 2011, Spirit used billboards and hand-held posters to advertise new service from Los Angeles, that contained an asterisk next to the advertised fare. On the billboards, the asterisk led to small print that stated additional taxes, fees and conditions would apply, but did not disclose the amount. The posters did not include any information about the taxes and fees. In addition, Spirit sent Twitter feeds announcing one-way fares for $9. A consumer who clicked on the link was taken to a second Webpage where the carrier disclosed for the first time that the fare did not include all taxes and fees, and that to qualify, a roundtrip ticket had to be purchased. Only after clicking on another link was the amount of additional taxes and fees disclosed.

“Consumers have a right to know the full price they will be paying when they buy an airline ticket,” U.S. Transportation Secretary Ray LaHood said in a press statement. “We expect airlines to treat their passengers fairly, and we will take enforcement action when they violate our price advertising rules.”

As we've reported in Best & Worst Airlines, the proliferation of fees has been a major source of aggravation to airline passengers.

DOT Fines Spirit Airlines for Violating Price Advertising Rules [DOT]