Cupertino, Calif. -- The Department of Justice said on Wednesday it has filed an antitrust lawsuit against Cupertino-based Apple and five book publishers, alleging the companies reached a deal to fix the prices of e-books. Three of the publishers -- Simon & Schuster, Hachette and HarperCollins -- already have reached settlements in their cases. According to the suit, the companies agreed to raise the prices of their e-books prior to the 2010 release of the iPad, and guarantee Apple a 30% commission on each unit sold. The publishers allegedly also agreed to offer their lowest prices to Apple, helping the company gain market share from Amazon. "Defendants' ongoing conspiracy and agreement have caused e-book consumers to pay tens of millions of dollars more for e-books than they otherwise would have paid," the suit alleges. Other publishers named include Penguin Group and Macmillan.