The United States court overseeing national security investigations has called for the declassification and publishing of documents related to the government's Prism data collection program.

The case documents date back at least to 2008 when the court issued an order reportedly requiring internet giant Yahoo to allow the government to obtain access to customer data.

The existence of Prism was revealed by former NSA contractor Edward Snowden.

In a statement, Yahoo says the release of the documents will "contribute constructively to the ongoing public discussion around online privacy".

Yahoo asked the court on 14 June 2013 to release documents about the program, shortly after revelations of the vast project.

It took legal action demonstrating its objections, and with substantial consumer backlash, to government requests to hand over data.

People carrying mobile phones walk past a banner supporting Edward Snowden in Hong Kong's financial Central district. ( Bobby Yip: Reuters ) Other Internet companies including Google and Microsoft have also sought declassification of documents.

The companies have stated they release information only in response to specific court orders.

Other top Internet and technology companies have faced consumer backlash since word leaked of the vast, covert surveillance program that US authorities insist only targets foreign terror suspects.

The Foreign Intelligence Surveillance Court says the government should review which documents should be declassified and inform the court of its decision by 29 July.

Judge Reggie Walton told the Justice Department it should address the matter with "priority".

ABC/AFP