U.S. District Judge Denise Cote said in a 159-page ruling collusion among the five publishers -- Hachette, HarperCollins, MacMillan, Penguin and Simon and Schuster -- would not have been possible without help from Apple, which has denied it participated in the price-fixing arrangement.
The ruling said Apple was not only a participant, but it was the pivotal player in the plot in which the companies attempted to use a new pricing arrangement to derail the pricing advantage enjoyed by Amazon.com, which had a lion's share of the e-book market and was the trendsetter on pricing.
"Without Apple's orchestration of this conspiracy, it would not have succeeded as it did," Cote wrote in her decision.
ABC News reported Apple spokesman Tom Neumayr said Apple's goal was to give consumers more choices.
"Apple did not conspire to fix e-book pricing and we will continue to fight against these false accusations," Neumayr said in a statement.
"When we introduced the iBookstore in 2010, we gave customers more choice, injecting much needed innovation and competition into the market, breaking Amazon's monopolistic grip on the publishing industry," the statement said.
"We've done nothing wrong and we will appeal the judge's decision," Neumayr said.
Judge Cote, however, has ordered a trial to determine damages.
The decision, was "a victory for millions of consumers who choose to read books electronically," said Bill Baer, assistant attorney general in charge of the Department of Justice's Antitrust Division.
"Through today's court decision and previous settlements with five major publishers, consumers are again benefiting from retail price competition and paying less for their e-books," Baer said.