Microsoft has launched a scathing attack on Google, saying the search giant's rival book-scanning service "systematically violates copyright".
Users can download pages from thousands of books
Since December, Microsoft's project - Live Search Books - has allowed users to access certain publications which were no longer under copyright.
However, Google allows snippets of copyrighted works to be seen on the web on its Google Books Search.
A Microsoft lawyer has accused Google of cutting into authors' profits.
'Raking in billions'
Google plans to scan millions of books and journals from libraries around the world and make them available.
However, Microsoft lawyer Thomas Rubin has said that by doing this without seeking permission, Google has left itself wide open to the accusation of copyright infringement.
"Companies that create no content of their own, and make money solely on the backs of other people's content, are raking in billions through advertising revenue and IPOs," Mr Rubin told a meeting of the Association of American publishers in New York.
"Google takes the position that everything may be freely copied unless the copyright owner notifies Google and tells it to stop."
Mr Rubin said that the acquisition of YouTube - which has featured large amounts of copyrighted material - showed Google's track record of protecting copyrights in other parts of its business was "weak" at best.
"Anyone who visits YouTube, which Google purchased last year, will immediately recognise that it follows a similar cavalier approach to copyright," he said.
The publishers' group - along with a writers' trade body, the Authors' Guild - is involved in a long-running legal action against Google.
The BBC's Guto Harri in New York says the latest comments by Microsoft's general counsel are a blatant and bitter attack on a rival which claims to be on a mission to do no evil.
Google defended its position, saying it complied with international copyright laws when it helped its users find information and that it worked with more than 10,000 partners to make books searchable online.
"The result has been more exposure and in many cases, more revenue for authors, publishers and producers of content," said Google's chief legal officer David Drummond.
Rivalries between Microsoft and Google are intensifying.
Microsoft has stepped up its internet search business while Google is making web-based software such as word processing, spreadsheets and email available in competition to Microsoft's off-the-shelf software.