STATE SECRETS

Another potential roadblock for the groups is that the government could try to assert what is known as the state secrets privilege, saying that continuing with the lawsuit would expose classified information, said Carrie Cordero, director of national security studies at Georgetown University Law Center.

Tretikov and Wikipedia founder Jimmy Wales wrote in the New York Times' opinion pages that they were concerned about where data on their users ends up after it is collected in bulk by the NSA. Citing close intelligence ties between the United States and Egypt, they said a user in Egypt would have reason to fear reprisal if she edited a page about the country's political opposition.

The US Supreme Court in 2013 rejected another challenge to NSA surveillance of email and other communications, ruling that a similar coalition of plaintiffs did not prove they had been spied upon or would be.

The ruling, however, was made just three months before the first of Snowden's revelations. Documents made public by Snowden support the right to sue, said Patrick Toomey, one of the American Civil Liberties Union lawyers working on the lawsuit.

Toomey said that with upstream collection, the NSA systematically taps into Internet message traffic between US and overseas users as it moves in and out of the United States over fiber-optic cables.

The NSA then systematically sweeps through the vast amount of content for anything relating to specific individuals or groups considered by US agencies to be intelligence targets, according to the documents leaked by Snowden.

Consequently, Toomey said, anyone inside the United States who sends or receives messages via the Internet to or from someone outside the country is likely to have had messages examined in some way by NSA.