The European Union's antitrust watchdog is probing whether Apple helped five major publishing houses illegally raise prices for e-books when it launched its iPad tablet and iBookstore in 2010.

The European Commission (EC) has opened formal antitrust proceedings to investigate whether international publishers Hachette Livre (Lagardere Publishing, France), Harper Collins (News Corp., USA), Simon & Schuster (CBS Corp., USA), Penguin (Pearson Group, United Kingdom) and Verlagsgruppe Georg von Holzbrinck (owner of inter alia Macmillan, Germany) have, possibly with the help of Apple, engaged in anti-competitive practices affecting the sale of e-books in the European Economic Area (EEA), in breach of EU antitrust rules.

The opening of proceedings means that the EC will treat the case as a matter of priority and does not prejudge the outcome of the investigation.

The Commission will 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 the EU or in the EEA. The Commission is also examining the character and terms of the agency agreements entered into by the above named five publishers and retailers for the sale of e-books.

"The Commission has concerns, that these practices may breach EU antitrust rules that prohibit cartels and restrictive business practices," the regulator said in a strtement.

The duration of antitrust investigations depends on a number of factors, including the complexity of each case, the extent to which the undertakings concerned cooperate with the Commission and the exercise of the rights of defence.