The European Union Commission said Monday it has opened two separate antitrust probes into seven airlines on suspicion that they may have operated an illegal cartel on transatlantic routes.

It said it suspects that some airlines under the broader Star Alliance 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), Deutsche Lufthansa (LHA.XE) and United Airlines (UAUA).

The second investigation is into proposed deals between the members of the Oneworld Alliance - American Airlines (AMR), British Airways (BAY.LN) and Iberia (IBLA.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 that prompted the European Commission's 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.

The airline alliances have traditionally been accepted by the regulators on both sides of the Atlantic as a certain amount of cooperation brings increased benefits to consumers in terms of more flexible routes and scheduling, and joint ventures were often impossible on nationalistic grounds.

However many travel groups complain that the recent scope of immunity granted in the U.S. to the alliances is too broad allowing the airlines to operate a pricing cartel.

In the U.S., the alliances have recently come under scrutiny from the House of Representatives transportation committee, which is proposing a bill that would unwind the existing system of global alliances.

Committee Chairman Rep. James Oberstar has said the alliances have become too dominant in the marketplace, with too much control over passenger fares.

In the U.S., airline alliances can apply for antitrust immunity that protects them from regulators. Star Alliance currently enjoys such immunity for some of the partners to jointly set prices and schedules across the Atlantic.

But the probe is likely to prove tricky for Continental Airlines, which is in the process of switching from rival alliance SkyTeam to Star and needs renewed antitrust immunity to work more closely with United.

Oneworld Alliance, the smallest of the three groupings that dominate transatlantic flights, is also trying to win immunity in the U.S.

The investigation comes a year after the "Open Skies" agreement between the European Union and U.S., which aimed to enable more airlines to start transatlantic routes

"This is a normal part of the E.U. process of examining our antitrust immunity application with American Airlines and Iberia," British Airways said in a statement.

However, the commission's antitrust spokesman Jonathan Todd said it was misleading to call the investigation a routine inspection.

We are investigating this as a matter of priority to "assess whether there is a violation of antitrust rules," Todd added.

Iberia said that the airlines were waiting for the approval from Brussels before starting more intensive cooperation.

Lufthansa spokesman said the company is in "constructive talks" with the European Commission, but that it will stick to its plans to implement the cooperation with its Star Alliance partners as quickly as possible, despite the investigation launched by the E.U. If found guilty, the commission can fine the companies up to 10% of their global revenue and demand they make changes to their business practices.

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