The United States' secret Foreign Intelligence Surveillance Court, or FISA court, has ruled to declassify a series of key documents intended to disclose the government's legal justification for their widespread, covert data collection program, PRISM.

FISA Court Judge Reggie Walton issued the ruling Monday in response to a challenge by internet giant Yahoo, who filed court papers last month in an effort to prove how "vehemently [Yahoo] had objected to government requests to hand over data," BBC reports.

The exposed documents include the transcript from a "key 2008 court case" which, according to BBC, was "widely seen as pivotal in letting the [National Security Agency (NSA)] establish PRISM and start gathering data on web use."

According to a series of slides revealed by NSA whistleblower Edward Snowden and reported on by the Guardian, under the data collection program, internet companies are compelled to grant the NSA access to materials including search history, the content of emails, file transfers and live chats.

As Guardian reporters Glenn Greenwald and Ewan MacAskill wrote at the time of the disclosure,

Companies are legally obliged to comply with requests for users' communications under US law, but the PRISM program allows the intelligence services direct access to the companies' servers. The NSA document notes the operations have "assistance of communications providers in the US."

"It remains to be seen how forthcoming (the government) will be," said Mark Rumold, a staff attorney at the Electronic Frontier Foundation, which on Tuesday also filed suit against the NSA on behalf of a broad coalition for violating the plaintiff's First, Fourth and Fifth Amendment rights.

"The administration has said they want a debate about the propriety of the surveillance, but they haven't really provided information to inform that debate. So declassifying these opinions is a very important place to start," he added.

"Once those documents are made public, we believe they will contribute constructively to the ongoing public discussion around online privacy," Yahoo said in a statement following the ruling.

The order requires the government to review which portions of the opinion, briefs and arguments can be declassified and report back to the court by July 29, AP reports.

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