By Maggie Shiels
Technology reporter, BBC News, Silicon Valley
One of Google's aims is to "bring the world's lost literature back to life"
The battle over Google's effort to digitise the world's books and create a vast online library has intensified.
Authors have until Friday to opt out of the $125m settlement the search giant made with authors and publishers.
The date for comments to the New York court overseeing the class action suit was extended from Friday to Tuesday, after the filing system went down.
As time ticks away, supporters and critics have been manning both sides of the debate to win the public case.
The settlement reached last October stemmed from a 2005 legal suit that Google faced for scanning out-of-print works without explicit permission from rights holders.
If approved by a judge, Google would create a Book Rights Registry where authors and publishers could register works and be compensated.
The US Student Association says access is the key in this settlement
Ahead of Friday's opt-out for authors, Google lined up a number of professors, students and civil rights activists who support the deal.
"We see access to knowledge as a civil right," Wade Henderson, president and chief executive of the Leadership Conference on Civil Rights, told reporters in a conference call.
"Information enables individuals to learn, to create and to pursue their dreams. Access to knowledge defines the meaning of equal opportunity in a democratic society," said Mr Henderson.
Access was also the issue that led the United States Student Association to throw its weight behind the Google books programme.
"Today, millions of books are accessible only to the privileged few who are accepted to universities and can actually afford to attend," said association president Gregory Cendana.
"With Google books, any student anywhere in the US will have the books in the greatest libraries of the world at their fingertips."
The most vocal critics of the deal have largely banded together to form the Open Book Alliance. It was set up by the non-profit Internet Archive, which has its own book-scanning project and has to date digitised 500,000 books.
Amazon is one of the big names trying to kill the Google books deal
"Just as Gutenberg's invention of the printing press more than 700 years ago ushered in a new era of knowledge sharing, the mass digitisation of books promises to revolutionise how we read and discover books," said Peter Brantley of the alliance.
"But a digital library controlled by a single company and small group of publishers would inevitably lead to higher prices and subpar services for consumers, libraries, scholars and students."
Technology giants Yahoo, Microsoft and Amazon are part of the coalition along with a number of libraries and writers and journalists groups.
Amazon, which competes with Google by scanning books to sell through its electronic Kindle reader, filed its own statement against the deal this week.
"It is unfair to authors, publishers and others whose works would be the subject of a compulsory licence for the life of the copyright in favour of Google and the newly created Book Rights Registry," it stated.
'Fact, not fiction'
The settlement is being examined by the Department of Justice which is also deciding whether to oppose the agreement.
Critics are concerned about everything from privacy to pricing
"We'll work to ensure that the privacy of online readers is fact, not fiction," said FTC chairman Jon Leibowitz.
Many believe the issue of rights over out-of-print books would best be solved by legislation and not the courts.
"It is never a good thing for private parties to make deals for the public good," said Martin Manley, the founder of Alibris.com, an online store which sells used, rare and out-of-print books.
"The public good is meant to be solved by regulators who are somewhat accountable and by legislators who are wholly accountable," Mr Manley told BBC News.
A final court hearing on the settlement is planned for 7 October.