Five US publishers are being threatened with legal action over the way they set prices for electronic books, reports the Wall Street Journal.
The US Department of Justice (DoJ) said the five had conspired to raise the prices of ebooks.
Also included in the legal threat is electronics firm Apple because of its role in the way ebooks are priced.
The threat comes as the publishers negotiate with the DoJ about the pricing model for electronic books.
The five publishers are; Simon and Schuster, Hachette, the US arm of Penguin, Macmillan and HarperCollins Inc.