"There is a substantial problem in the industry," said EU Consumer Commissioner Meglena Kuneva after investigators checked more than 400 Web sites through much of the 27-nation bloc. "Over 50 percent of sites checked seem to mislead consumers."
Allegedly cheap tickets are often leaden with hefty charges. Kuneva said investigators found offers for 20 euros only to find out five pages further on that the total price was over 100 euros.
Sometimes there simply are no flights for the lowest prices advertised or insurance is automatically added to the price.
Belgium came out worst, with 46 of the 48 sites showing irregularities. Of the 15 EU nations checked, only Austria, Cyprus and Greece had a clean bill of health in the test of airline and travel Web sites.
Kuneva said Web site operators had until the end of January to clean up their act or face fines or closure.
EU airline travel accounts for some 700 million passengers a year and it is one of the areas with most consumer complaints. In all, 447 sites were checked and 226 showed irregularities. Misleading pricing was the most prevalent problem.
Jim Murray, the head of the BEUC consumer advocacy group, welcomed the initiative and hoped "it will be the first of many" to counter illegal practices affecting consumers across Europe.
France, where irregularities were found in 13 of 31 cases, said it would take immediate action since some of the sites did not use French, in addition to the additional charges and misleading advertising.
The 60-carrier European Regions Airline Association underscored the need for transparency on Web sites, but it balked at plans by the European Parliament to demand that airline prices include a detailed breakdown of costs, including airport security and fuel surcharges.
"This is absurd bureaucracy and will confuse passengers," said spokesman Andy Clarke. He argued hotel guests are not interested in heating costs or security expenses in their bill. "Why do Europe's lawmakers believe that you have different needs when you fly?" he asked.