The airline was put on the EU's "black list" – along with Turkish, Royal Air Maroc, Aeroflot, Northwest and Olympic.
The EU's 18-month crackdown found misleading adverts and unfair practices reported on 137 airline websites in 15 EU countries, plus Norway.
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Many of the complaints refer to deceptive "headline" prices, which disguise hidden extra costs.
To comply with EU consumer protection rules, websites were judged according to a 14-point check list, which asked if all such extras such as taxes, charges and fees were included, and if extra costs were added as opt-in or opt-out options.
While 115 of the offending websites have since agreed to comply with EU rules, the nine airlines either ignored or responded inadequately to the EU's complaints, said EU Consumer Protection Commissioner Meglena Kuneva.
"This a signal that they do not care about their customers," Kuneva said.
However officials pointed to the fact that the vast majority of airlines – 52 out of 67 – have either been given a "clean bill of health", or have promptly committed themselves to addressing the issues raised.
That list now includes previous offenders such as low-cost carrier Ryanair and Austrian Airlines.
"This first pan-European enforcement investigation has shown it has real teeth and can deliver," Kuneva said.
The European Commission, which launched its investigation in September 2007, has given persistent offenders until July to remedy the situation or face the wrath of national regulators.
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