The secret US court that rules on snooping activities by the country's agencies has granted the Yahoo! motion to reveal its 2008 decision justifying the PRISM project.
The Foreign Intelligence Surveillance Court said in its order that it has handed over its opinion document and the legal briefs that were submitted by the parties to the government for a "declassification review". The documents are likely to be released to the public "in a form that redacts any properly classified information".
The government is expected to decide by 26 August which parts of the opinion, given in 2008, can be published, a separate court filing from the Department of Justice said.
NSA whistleblower Edward Snowden first revealed the existence of the PRISM project, which allowed the US to spy on phone and internet communications through their metadata, last month. After the programme was outed, the Director of National Intelligence allowed some information about it to be declassified and revealed to the public.
Internet firms like Yahoo!, Google and Microsoft have pushed for more disclosures, however. They claim the cyber-snooping wasn't as bad as everyone thinks it was and are hoping that any challenges they made to handing over their customers' data might buff their rather tarnished reputations.
The ruling that is due to be revealed, which came after Yahoo! questioned whether it had to comply with PRISM, will lay out the legal justifications for the programme. Yahoo! said in a statement seen by Reuters that it was "very pleased" that the court was willing to release its redacted opinion.
"Once those documents are made public, we believe they will contribute constructively to the ongoing public discussion around online privacy," the firm said.
Microsoft asked US Attorney General Eric Holder in a letter published yesterday for more freedom to discuss what information it hands over to the NSA.
"Numerous documents are now in the public domain. As a result, there is no longer a compelling government interest in stopping those of us with knowledge from sharing more information, especially when this information is likely to help allay public concerns," Microsoft general counsel Brad Smith wrote. ®