The United States Department of Justice (DOJ) has accused Apple, along with five publishing companies, of conspiring to fix the price of e-books.
US attorney general Eric Holder said their investigations suggest the firms conspired to artificially inflate the price of electronic books.
Three of the publishers have already agreed to a settlement, leaving Apple and two publishers as the remaining defendants.
"In recent years, we have seen the rapid growth – and the many benefits – of electronic books. E-books are transforming our daily lives, and improving how information and content is shared," Holder said.
"For the growing number of Americans who want to take advantage of this new technology, the Department of Justice is committed to ensuring that e-books are as affordable as possible."
The suit centres on the business model Apple uses to compensate publishers for sales.
By taking a 30 per cent cut from sales, the DoJ believes the publishers are forced to mandate the retail price for their titles.
The suit alleges that the practice is anti-competitive and takes away the right of individual merchants to dictate the sales price of media.
Apple's business model has long been the subject of scrutiny in the publishing space.
In addition to the DoJ probe and suit, Apple is the focus of a European Commission probe into possible anti-trust violations.
The DoJ also alleges that Apple met with publishers every quarter in an effort to conspire to maintain higher prices and disclose confidential details on the business models used by rival e-book services, including Amazon.
"Beginning in the summer of 2009, we allege that executives at the highest levels of the companies included in today's lawsuit, concerned that e-book sellers had reduced prices, worked together to eliminate competition among stores selling e-books, ultimately increasing prices for consumers," Holder said.
"As a result of this alleged conspiracy, we believe that consumers paid millions of dollars more for some of the most popular titles."
V3 contacted Apple for a response to the allegations but the firm declined to comment.
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