MIRAMAR, Fla. (CBSMiami.com) – South Florida-based Spirit Airlines is known for its countless fees, but Spirit will be the one paying up after it was fined by the U.S. Department of Transportation Monday.

The DOT fined Spirit $50,000 for “violating federal aviation laws and the Department’s rules prohibiting deceptive price advertising in air travel.”

Spirit was slapped with the fines after the DOT said that in June, Spirit used billboards, hand-held posters, and tweets to advertise new fares to Los Angeles. The DOT said the billboards never disclosed how much the additional taxes, fees, and conditions would be, in violation of Department rules.

The poster did not include any information about the taxes and fees, while the tweets took users to a page on Spirit’s website where the airline disclosed for the first time the fares didn’t include all taxes and fees and you had to buy a roundtrip ticket to qualify for the fares as low as $9.

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

New DOT rules requiring airlines to include all government taxes and fees in every advertised fare will kick in on January 24, 2012.