Yahoo has won the release of 1,500 pages of documents from a key 2008 case in a secretive US surveillance court.
The documents relate to a Foreign Intelligence Surveillance Court (FISC) case in which Yahoo attempted to challenge US National Security Agency (NSA) demands for customer information as unconstitutional.
But the FISC ordered Yahoo to hand over the user data requested by the government.
The newly unsealed documents show that the court threatened to fine Yahoo $250,000 a day if it failed to comply.
The case was subsequently used by the US government to persuade tech companies to co-operate with the NSA’s Prism programme, revealed by whistleblower Edward Snowden in June 2013.
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Snowden’s revelations linked Yahoo and eight other top technology companies to Prism, prompting Yahoo to call for the publication of the documents.
Yahoo said the released documents underscore how the company has had to “fight every step of the way” to challenge US government surveillance.
“Now that the FISC-R [court of review] has agreed to unseal the proceedings at our request, we are working to make these documents available,” read the announcement by Ron Bell, Yahoo's lawyer.
“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,” he said.
But Bell added that, despite the declassification and release, portions of the documents remain sealed and classified.
Yahoo is still pushing for the FISC to release materials from the case in the lower court.
“We will continue to contest requests and laws that we consider unlawful, unclear or overbroad,” Bell’s announcement concluded.