U.S. Circuit Judge Denny Chin in Manhattan also rejected Google's bid to dismiss claims by The Authors Guild and several groups representing photographers and graphic artists, which would have forced their members to sue individually.
Plaintiffs in the seven-year-old case have complained that Google's plan for the library, which would include millions of out-of-print works, amounted to "massive copyright infringement."
The case arose from Google's 2004 agreement with several big research libraries to digitally copy books and other writings for its Google Books website, with a goal of helping researchers and the general public locate the materials.
Google has since scanned more than 12 million books, but planned to provide only snippets online, saying this activity constituted "fair use" under U.S. copyright law.
Fighting the pages
Chin said it would be more efficient for authors to sue as a group, rather than risk disparate results and the "exponentially" higher costs of individual lawsuits.
He also said it would be unjust to force members of The Authors Guild, the American Society of Media Photographers and other groups to sue individually "given the sweeping and undiscriminating nature of Google's unauthorized copying."
The litigation combines lawsuits against Mountain View, California-based Google in 2005 on behalf of authors, and in 2010 on behalf of photographers and graphic artists.
A Google spokeswoman said in an emailed statement: "As we've said all along, we are confident that Google Books is fully compliant with copyright law."
Lawyers for the plaintiffs did not immediately respond to requests for comment.
In March 2011, Chin cited antitrust and copyright concerns in rejecting a proposed comprehensive $125 million settlement, saying it went "too far" in letting Google effectively conduct "wholesale copying of copyrighted works without permission."
Chin was elevated in 2010 to the federal appeals court in New York, but kept jurisdiction over the Google case, which he had begun overseeing as a trial judge.