Google has argued that its Books Library Project for which the company has scanned millions of books and made them available online without authors' permission does not violate copyright laws.
Plaintiffs in the case - The Authors Guild along with photographer and graphic artist groups - are claiming that the project is a massive copyright infringement and are seeking damages and royalties.
"Google has engaged in a massive campaign of bulk copying of books, which could adversely affect actual and potential markets for copyrighted books," the groups said in a court brief.
Since 2004, Google has scanned over 20 million books following agreements made with libraries across the world to digitise books.
The company is arguing that the project is protected under the "fair use" exception of the US copyright act as it only makes sections of the books accessible online.
"Plaintiffs have adduced no evidence that Google Books has displaced the sale of even a single book," Google said in its brief. "A survey of authors has shown that the majority of authors approve of their inclusion in Google Books."
If Google loses the case, the company could be forced to pay over $3 billion in damages and end the project, which has cost it around $40 million a year.
On Monday, however US Circuit Judge Denny Chin suggested that he may be inclined to side with Google, by citing a number of examples in which the project has enabled people to get information, including his clerks.
"Aren't these transformative uses, and don't they benefit society?" said Chin. He also suggested that Google could help boost sales through the project and noted examples of consumers purchasing books after finding information through the search engine's feature.
Edward Rosenthal, a lawyer for the claimants, said the project, "may benefit society in some instances," but the copyright holder should retain the choice as to whether the work is made available.
He added that Google is "a copy shop for the 21st Century," arguing that in itself, copying a books violates copyright laws, and so the authors should be compensated at the very least.
Judge Chin has not said when he will rule on the case.