Three groups representing US authors have objected to a revised industry settlement with Google that seeks to clear the way for millions of books to be digitised and sold online.
Google and the Authors Guild and the Association of American Publishers revised the settlement in November in response to US Department of Justice concerns over copyright.
But the National Writers Union, the American Society of Journalists and Authors and the Science Fiction and Fantasy Writers of America say the amended version is also no good.
The three groups have appealed in an open letter to 60 members of the US Congress who are also authors, to encourage the DoJ to continue its opposition to the Google Books settlement.
In the letter, the groups claim that their interests are not being fairly represented by the Authors Guild.
The move comes after author Ursula Le Guin resigned from the Authors Guild, accusing the group of abandoning the concept of copyright without a struggle for the sake of its partnership with Google.
The authors of the letter criticise the settlement on various points, including the lack of notice to authors, the complexity in opting out, and the new regulatory board that overrides individual contracts.
"The amended version of the settlement still creates a de facto monopoly for Google at the expense of all Americans," the letter said
The letter calls for the DoJ's continued close scrutiny of the settlement. A hearing on the fairness of the revised settlement is scheduled for 18 February.