Technology giant Apple and major book publishers are being sued by the US Department of Justice over the pricing of e-books.
The US accuses Apple and Hachette, HarperCollins, Macmillan, Simon and Schuster and Penguin of colluding over the prices of e-books they sell.
This lawsuit is over the firms' move to the agency model where publishers rather than sellers set prices.
But Hachette, HarperCollins and Simon and Schuster have already settled.
The case will proceed against Apple, Macmillan and Penguin "for conspiring to end e-book retailers' freedom to compete on price", the Justice Department said.
"As a result of this alleged conspiracy, we believe that consumers paid millions of dollars more for some of the most popular titles," Attorney General Eric Holder said.
'Effectuate their conspiracy'
"To effectuate（完成，实行） their conspiracy, the publisher defendants teamed up with defendant Apple, which shared the same goal of restraining retail price competition in the sale of e-books," according to papers filed in New York's Southern District court on Wednesday morning.
"Apple facilitated the publisher defendants' collective effort to end retail price competition by coordinating their transition to an agency model across all retailers."
Apple, which sells books through its iBooks platform on the iPad and iPhone, declined to comment.
Hachette said that it remained "confident that we did not violate the anti-trust laws" while adding it "reluctantly" joined the settlement.
But Macmillan's chief executive, John Sargent, said "the terms the DOJ demanded were too onerous" to settle and would allow Amazon "to recover the monopoly position it had been building before our switch to the agency model".
Meanwhile, the European Commission has also been probing e-book price fixing.
Apple, Hachette, HarperCollins, Macmillan and Simon and Schuster have now made proposals to settle that probe.
"The European Commission has received proposals of possible commitments from Apple and four international publishers," said the EU's competition commissioner Joaquin Almunia.
"I welcome the fact that these five companies are making proposals to reach an early resolution of the case, so promptly after we opened proceedings in December 2011," he added.