Surveillance scheme terror warning
The White House and congressional backers of the National Security Agency's (NSA) surveillance programme have warned that ending the collection of phone records from millions of Americans would put the US at risk from another terrorist attack.
With a high-stakes showdown vote looming in the House of Representatives, White House press secretary Jay Carney issued a statement on the eve of Wednesday's vote.
The measure by Republican representative Justin Amash would end the secret programme's authority, an action that Mr Carney contended would "hastily dismantle one of our intelligence community's counter-terrorism tools."
General Keith Alexander, head of the NSA, made a last-minute trip to Capitol Hill on Tuesday to urge politicians to reject the measure in separate, closed-door sessions with Republicans and Democrats.
Seven Republican committee chairmen issued a similar plea in a widely-circulated letter to their colleagues.
An unlikely coalition of libertarian-leaning conservatives and liberal Democrats say the programme amounts to unfettered domestic spying on Americans.
Mr Amash and Democratic representative John Conyers are the chief sponsors of an amendment that would end the ability of the NSA to collect phone records and metadata under the USA Patriot Act unless it identifies an individual under investigation.
Mr Amash said his measure tries to rein in the NSA's blanket authority. Responding to the White House statement, the congressman tweeted late on Tuesday: "Pres Obama opposes my #NSA amendment, but American people overwhelmingly support it. Will your Rep stand with the WH or the Constitution?"
Republican leaders allowed the House to consider Mr Amash's amendment to a 598.3 billion dollar (£389.4 billion) defence spending bill for the fiscal year beginning October 1.
The vote would be the first time Congress has weighed in since former NSA systems analyst Edward Snowden leaked documents that revealed that the NSA had collected phone records, while a second NSA programme forced major Internet companies to turn over contents of communications to the government.