Amazon is trying to convince a federal judge to block the $125m settlement that will let Google Books make out-of-print works available online.

Amazon’s opposition was made public last week when it joined the Open Book Alliance, notes C/Net. Now Amazon has filed its own brief with the U.S. District Court for the Southern District of New York, arguing against making the proposed settlement final.

In its filing (click for PDF), Amazon notes that it has also scanned books, but has not taken the controversial step that Google took in scanning out-of-print but copyright-protected books without explicit permission.

When Google began scanning books from libraries, it believed it had the right to scan the entire text of a copyright-protected book under fair-use laws so long as it only displayed a snippet of the contents. Authors groups and publishers vehemently disagreed, resulting in a class-action lawsuit and the proposed settlement at issue in this case.

At least two other Google rivals, Microsoft and Yahoo, are expected weigh in with their opposition.

The U.S. Justice Department, which is taking a look at Google’s book deal, has until Sept. 18 to share its thoughts on the case. That filing may provide a better indication whether Justice believes Google’s deal with authors and publishers would violate U.S. laws set up to prevent predatory pricing and promote competition, says USA Today.

According to a report from Forrester, the eBook and eReader market has now hit a point where it is ready to break out of its niche and become a mainstream phenomenon. But Forrester says an e-reader need to cost between $50 and $99 before most consumers would consider buying one.

Google is expected entry into the eBook market shortly, reports the NY Times. Google has already made its 1.5 million public-domain books available for reading on mobile phones as well as the Sony Reader, the Kindle’s largest competitor.