Google says the deal would give new access to out-of-print books
The US Justice Department has urged a New York court to reject a deal that would allow internet company Google to publish millions of books online.
The deal raised copyright and anti-trust issues, the department said, and should be rejected in its current form.
The court is due to rule on the issue early next month.
Under the deal - the product of a legal suit - Google would establish a $125m (£77m) fund to compensate those whose works it published online.
It would establish a Book Rights Registry so that authors whose work it digitised were paid when their material was viewed online.
The deal was agreed in October 2008 with the Authors Guild and the Association of American Publishers (AAP) after they sued Google for copyright infringement.
Companies including Microsoft, Amazon and Yahoo have all objected to the deal.
'More talks needed'
The US justice department said that the breadth of the settlement raised "significant legal concerns".
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Speaking as a researcher, I find Google Books a practical way to obtain information from rare books. But I do not want to read a novel online
In its present form it would, it said, give Google sole authority for books whose copyright holder could not be found and provide inadequate protection to foreign rights holders.
It also seemed to give publishers the power to restrict price competition and drive other digital distributors from the market, it said.
The court "should reject the proposed settlement in its current form and encourage the parties to continue negotiations to modify it", the department said in its submission.
In a statement, Google, the Authors Guild and the AAP said that they were "considering the points raised by the department and look forward to addressing them as the court proceedings continue".
Google says the deal would give readers unprecedented access to books that have been out of print for years.