Microsoft, Yahoo and Amazon have joined the Open Book Alliance (OBA) to add more weight to the campaign against Google's Book Search project.
The OBA is run by the Internet Archive, which has already digitised millions of books. Its main complaint is that Google has entered the book digitisation market in a way that makes it difficult for other organisations that offer similar services to compete.
Google has also digitised millions of books for its Book Search product, and signed a $125m (£76m) deal with book publishers last year that includes the founding of a Books Rights Registry to distribute revenue to authors and publishers.
The deal resolved a number of copyright issues raised by book publishers about Google's digitisation process, and the backing of major publishers means that the service could become the largest online portal of human knowledge, leading to concerns that it could breach the Sherman Antitrust Act.
The US Department of Justice (DoJ) issued a formal notice in July that its anti-trust division is investigating Google's deal with the publishers, and the OBA is currently lobbying the DoJ to take stronger action.
Microsoft has confirmed its involvement in the OBA, although it could not provide further insight on the reasons for its participation.
"Because the coalition's formal announcement is not expected until next week, we are referring those who seek additional comment to Peter Brandtley at the Internet Archive, which is leading this effort," said a Microsoft spokesman.
The Internet Archive, Yahoo and Amazon could not immediately be reached for comment on the matter.
A Google spokesman said: "The Google Books settlement is injecting more competition into the digital books space, so it's understandable why our competitors might fight hard to prevent more competition.
"That said, it's ironic that some of these complaints are coming from a company that abandoned its book digitisation effort because it lacked 'commercial intent'."
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