The US Senate is meeting in a rare weekend sitting to try to avert the expiry of key anti-terrorist laws that allow phone data to be collected by the security services.
Senators failed several times to pass a revised plan and to extend key provisions of the USA Patriot Act, which lapse at midnight (04:00 GMT).
The new measures have already been backed by the House of Representatives and the White House.
Sixty votes are needed in the Senate.
Ever since National Security Agency contractor Edward Snowden revealed that the phone records of tens of millions of Americans were being collected en masse by the NSA, the pressure to revise the programme has been intense, BBC Washington correspondent Gary O'Donoghue says.
A court has already ruled the practice illegal and the House has passed a new Freedom Act which would oblige phone companies to retain data and impose greater controls on how that data could be accessed.
http://www.bbc.com/news/world-us-canada-32950120