Around 60 airline ticket-sale websites are still breaking consumer laws, mostly by duping consumers over pricing.
A recently published report shows that the European Union is making slow progress in bringing recalcitrant sites to heel, despite a seven-month investigation.
"This report shows serious and persistent problems with ticket sales throughout the airline industry as a whole," said EU consumer commissioner Meglena Kuneva.
"I intend to work with member states to do everything possible to wrap up this investigation by [1 May 2009]."
The EU sweep of airline ticketing sites was launched in September 2007, involving 15 member states and Norway.
Each country's authorities were asked to check a total of 386 websites, of which 137 (run by 80 companies) were found to be misleading. Barely half of these have been corrected so far.
Misleading pricing was identified as the biggest problem in the original investigation, but many sites were found to have multiple breaches of consumer laws.
These included advertising special offers which were unavailable, pre-checked boxes which meant that consumers were buying optional features by default and contracts missing in some languages.
The problems are perpetrated by airlines and their ticketing agencies. Of the 79 sites investigated for misleading pricing, 44 were airlines, 27 were travel agencies and tour operators, and eight were others such as price comparison sites.
Legal constraints prevent member states from publishing the names of the companies under investigation.
