The documents released by Yahoo! shed new lights on the NSA’s secret surveillance program PRISM, which was previously leaked from the agency’s confidential documents provided by Global surveillance whistleblower and former National Security Agency contractor Edward Snowden .

The released documents underscore how we had to fight every step of the way to challenge the US Government’s surveillance efforts ,” the company’s general counsel Ron Bell said on Yahoo’s Tumblr page . “ At one point, the US Government threatened the imposition of $250,000 in fines per day if we refused to comply. ”

The US government threatened Internet giant with a $250,000 fine per day several years ago if it failed to comply with National Security Agency ’s notorious PRISM Surveillance program, according to unclassified court documents released by Yahoo! on Thursday.

PRISM allowed NSA to intercept and process not just the United States telecoms companies data including Verizon which has 98.9 million customers, but also some of the most widely used and major Internet firms including Microsoft, Google, Yahoo!, Facebook and Skype. However, Officials have said the deeply contentious program ended in 2011.

The Foreign Intelligence Surveillance Court (FISA) of Review, which provides legal authority in surveillance requests, released more than 1,500 pages of previously secret documents related to Yahoo!’s 2007 challenge to the government’s demand for data, according to Bell, who said that in 2007, the US government “amended a key law to demand user information from online services.“

“We refused to comply with what we viewed as unconstitutional and overbroad surveillance and challenged the US government’s authority,” Bell said.

But, Yahoo eventually lost that initial challenge and an appeal. The released documents underscore how Yahoo and others have been seeking to make public these court documents to show they were forced to comply with government requests and made every attempts to fight the US Government’s surveillance efforts, rather than simply acquiescing to them.

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“We consider this an important win for transparency and hope that these records help promote informed discussion about the relationship between privacy, due process, and intelligence gathering,” Bell added.

Users come first at Yahoo. We treat public safety with the utmost seriousness, but we are also committed to protecting users’ data. We will continue to contest requests and laws that we consider unlawful, unclear, or overbroad.”

The Christopher Soghoian, Principal Technologist at ACLU, points out the $250k-a-day fine, which means $90m (£55.42m) fine a year, seems cheap for the trust of users worldwide. As Yahoo!’s net income in 2008 was $424.3m.

Some parts of released documents remain classified and the Internet giant is still pressuring the court to agree to make those documents public, as well as other documents that are still classified.