BRUSSELS » The European Union’s antitrust watchdog is probing whether Apple and five major publishing houses have colluded to restrict competition in the market for e-books.

The European Commission probe announced Tuesday focuses on potentially anticompetitive practices by publishers Hachette Livre, a unit of France’s Lagardere Publishing; Harper Collins, owned by Rupert Murdoch’s U.S.-based News Corp.; CBS Corp.’s Simon & Schuster; Penguin, which is owned by U.K. publishing house Pearson Group; and Germany’s Verlagsgruppe Georg von Holtzbrinck.

"The Commission will in particular investigate whether these publishing groups and Apple have engaged in illegal agreements or practices that would have the object or the effect of restricting competition" in Europe, it said in a statement.

It is also looking into "agency agreements" between the publishers and the e-book retailers. In those agreements, publishers set a price for their e-books, with retailers taking a cut of the profits.

Apple Inc. runs the iBook online store, in which consumers can buy and download e-books onto the company’s devices, including the popular iPad tablet and the iPhone. It is a competitor of Amazon.com Inc.

The announcement from the Commission follows raids in the offices of several publishers in March and a related probe launched by the U.K. Office of Fair Trading. The Commission said Tuesday that the British agency OFT had suspended its investigation since the Commission had taken over the case, but the two regulators were working closely together.

Pearson said that the fact that the Commission has opened an investigation does not prejudge the outcome of the probe.

"Pearson does not believe it has breached any laws, and will continue to fully and openly cooperarte with the Commission," the company said in a statement.