Google is finding that its rivals aren't very willing to help it fight a copyright infringement suit regarding its plans to digitize books.

Yahoo joined Amazon in denying requests from Google to access information on how they make digital copies of books, the New York Times reports. Google had issued subpoenas to both firms, claiming it needs such information from rivals in order to fight a lawsuit filed last year by a group of publishers and the Authors Guild, which claim that Google did not get proper approval to digitize books and make them available online.

Google rivals Amazon, Yahoo and Microsoft say the subpoenas are an attempt by Google to steal trade secrets. Google said it was seeking "documents sufficient to show [rivals] possess the legal right to include each book" in any scanning project, along with information on how those companies viewed the issues of fair use and copyright, reports E-Commerce News.

Google has struck deals with some publishers to include their works in its digitization program, and has defended digitization by claiming it could boost book sales by allowing users to conduct keyword searches.

Google says users would not be able to download entire copies of copyright-protected books but would instead be referred to a site such as Amazon, or the publisher's own homepage, where the book could be purchased.