The European Union Commission said Monday it has launched two antitrust cases looking in to airline cooperation on transatlantic routes which could constitute an illegal cartel.

It said it suspects certain airlines under the broader Star and oneworld alliance banners have cooperated too closely on prices and capacity.

The first investigation concerns both existing and planned cooperation between members of the Star Alliance group - Air Canada (AC.A), Continental Airlines (CAL), Lufthansa (LHA.XE) and United Airlines (UAUA).

The second investigation is into proposed deals between three members of the Oneworld alliance - American Airlines (AMR), British Airways (BAY.LN) and Iberia (INLA.MC).

The level of cooperation between the two groupings of airlines "appears far more extensive than the general cooperation between these airlines and other airlines which are part of the Star and oneworld alliances," the commission said.

The agreements under scrutiny allow the airlines to coordinate their commercial, marketing and operational activities on routes between the European Union and North America.

The commission said it is concerned the airlines' plans to jointly manage schedules, capacity, pricing and revenue on transatlantic routes may lead to reduced competition on the routes.

-By Peppi Kiviniemi, Dow Jones Newswires; +32 (0)2 741 1483; peppi.kiviniemi@dowjones.com