The European Union’s antitrust group is investigating whether Apple and major publishing houses are guilty of colluding to cut back competition in the e-book market. In a statement, the European Commission announced a probe into five publishers — France’s Hachette Livre, Harper Collins, Simon & Schuster, Penguin and Germany’s Verlagsgruppe Georg von Holtzbrinck — and Apple.

The commission said that it’s looking at the agency agreements between publishers and e-book retailers that determine prices and the percentages that retailers gain from e-book sales.

“The Commission has concerns, that these practices may breach EU antitrust rules that prohibit cartels and restrictive business practices,” the agency said.

The announcement follows a series of unannounced raids that antitrust officials conducted on the e-book sector in March. At that time, the commission said that the inspections were a “preliminary step” into an investigation of anticompetitive practices.

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