(CNN) -- Budget airline Ryanair faces an investigation from the UK's consumer and competition authority following allegations of misleading and unfair advertising.
Ryanair has complained to OFT about its ongoing row with the UK's Advertising Standards Authority.
British advertising watchdog the Advertising Standards Authority has referred Europe's leading low-cost carrier to the Office of Fair Trading after it failed to act on a series of previous warnings over code breaches.
ASA had found the Irish airline guilty of seven transgressions in a two-year period, it said on its Web site.
It said Ryanair had exaggerated claims about the availability of flights at advertised prices, and it advertised prices that did not include taxes and charges.
The ASA was also unhappy with Ryanair's "misleading" comparisons with competitors, and that it did not display restrictions that would exclude customers from taking up an offer or provide evidence to prove the claims it was making.
"It is very disappointing, but absolutely necessary, that we have had to take this course of action," said ASA director general Christopher Graham, whose authority last referred a company to OFT in 2005.
"The ASA has given Ryanair every opportunity to put its house in order and ensure that its advertising adheres to the codes. Instead, they have continued to mislead consumers and denigrate competitors.
"We would prefer to work with advertisers within the self-regulatory system rather than call in a statutory body, but Ryanair's approach has left us with no option but to refer them to the OFT who will consider appropriate action."
Last week, Ryanair complained to OFT about its treatment by the ASA.
It said in a statement on its Web site that the ASA had "demonstrated a repeated lack of independence, impartiality or fairness where Ryanair is concerned by making factually inaccurate and untrue findings in response (in some cases) to totally baseless and unsubstantiated alleged complaints."
Ryanair's Peter Sherrard said the ASA had "clearly confirmed its bias and blind determination to rule against Ryanair's adverts."
In February, Ryanair had to shut down its Web site and call centers for three days while it upgraded its reservations system.
The airline said the move was necessary to make technical changes as it converts to a new system, but OFT indicated at the time that the shutdown was due to Ryanair's failure to meet a deadline to list all fares on the site.
A Ryanair spokesman said the airline was not forced by the OFT to shut down its system as a punitive measure. He said the Web site already complied with OFT requirements and simply required an updated system.
The OFT said it took action last year against 13 airlines that did not include "fixed non-optional costs" in prices on their Web sites. It said 11 airlines amended their sites to make those fees clear, but Ryanair and Ireland's Aer Lingus asked for extra time.
Aer Lingus met the new deadline, the OFT said, but Ryanair did not.
Ryanair has previously been in trouble over adverts, including one depicting French President Nicolas Sarkozy and Carla Bruni before their wedding, and another showing a scantily-clad schoolgirl. E-mail to a friend