The US Senate is holding a rare Sunday session to try to break an impasse over reforms to the Patriot Act. Failure to do so would mean that some of the NSA's snooping methods would be illegal as of midnight.
Majority leader Mitch McConnell called the lawmakers back to Washington to try to thrash out a remedy to the dispute, despite the fact that fellow Kentucky Senator Rand Paul has pledged to block any solution.
The bill that has already been passed by the House of Representatives and is supported by the White House needs 60 votes to pass in the Senate, but it appears to be three votes short. On May 23, the last attempt by the Senate to pass the legislation failed by a vote of 57-42.
The proposed law would scale back the powers or the National Security Agency, forcing it to stop a programme in which it collects the telephone metadata of Americans en masse, even if they have no known connection to terrorists.
Metadata includes several types of information such as the numbers someone has called, the times phone calls were made and their duration but not the actual content of the conversations.
'Illegal NSA activities'
Earlier this month, a Manhattan court judge ruled the practice illegal, but stopped short of ordering the NSA to cease such surveillance, as the Patriot Act was set to expire this weeks later - this Sunday at midnight local time in Washington (0400 UTC).
But Senator Paul has said he is dead set against the reform bill and is determined to do all he can to stop it.
"I will force the expiration of the NSA illegal spy program," Paul said in a statement released via Twitter on Saturday. "Sometimes when the problem is big enough, you just have to start over."
Under the Senate's complicated rules, Paul does have the power to prevent the issue from coming to a vote, at least temporarily.
US President Barack Obama used his weekly radio address on Saturday to appeal to the Senate to pass the bill, and to accuse "some folks of trying to use this debate to score political points." Obama also pointed out that with the expiry of the Patriot Act, not only would the bulk collection of metadata become illegal, but so would other "tools" designed to prevent terrorist attacks.
Shutting it down
The NSA has said that it has already begun winding down the metadata collection program in the expectation that there will be no extension of its current powers. It said it would begin shutting down the servers that carry it out at 3.59 p.m. local time on Sunday, to ensure that the program had completely ceased before the legal framework that has allowed it to do so expires.
The NSA program had been secret until it was revealed by former NSA contractor Edward Snowden almost two years ago. The revelations caused an uproar in Germany, particularly the news that the NSA had tapped into Chancellor Angela Merkel's mobile phone.
pfd/bw (AP, Reuters, AFP, dpa)