An investigation by the European Union found that buying airline tickets online is still fraught with risk, and a third of consumers are "ripped off or misled and confused."

It warned that if the offending airlines and other ticket sellers don't improve their sales and marketing practices by May 1, 2009, the European Commission "will have no choice but to intervene." Last year, the E.U. surveyed 386 sites in 13 E.U. countries and in Norway and found that 137 of them were misleading consumers or using unfair practices. But over the last seven months, only half of the Web sites that were in violation have "cleaned up their act," the E.U. said.

The findings came to light as part of a "sweep," a systematic check carried out in different countries simultaneously to investigate breaches in consumer law. Many sites had multiple problems, according to the E.U.

The biggest problem is misleading pricing, found in 58% of the sites under investigation. Irregularities related to contract terms, such as pre-checked boxes for optional services, were found in 49%, and non-availability of advertised offers was a problem in 15% of the sites.

The 137 Web sites under investigation represent about 80 companies, including some "large brand names," the E.U. said. Compliance differed widely between national and cross-border cases.

The report shows a 55% enforcement/correction rate for national sites, where authorities are dealing with companies based in their own countries, and a 12% enforcement/correction rate for cross-border cases, where national authorities request assistance from authorities in other member states.

The E.U. noted that legal constraints prevent most member states from publishing company names while administrative or legal proceedings are ongoing.