Senator Rand Paul, a possible Republican presidential candidate, has sued the Obama administration over the National Security Agency's mass collection of millions of Americans' phone records.
The senator said he and activist group FreedomWorks filed the suit on Wednesday for themselves and on behalf of "everyone in America that has a phone".
The lawsuit argues that the bulk collection programme that has been in existence since 2006 violates the US Constitution's Fourth Amendment right against unreasonable searches. It calls for an end to the programme, which was revealed by former National Security Agency analyst Edward Snowden.
The Obama administration maintains that the programme, begun under then-president George W Bush, is legal. Courts have largely sided with the government.
President Barack Obama has called for reforms to the programme in an effort to regain public trust. Others, like Paul, have called for the end of such surveillance.
Paul dodged a question about his presidential ambitions during a news conference on Wednesday. But his lawsuit is the latest effort to propel the debate over the once-secret surveillance programme into the 2016 presidential campaign.
The surveillance debate has exposed internal Republican tensions. The party has split over the issue, with its leadership backing the programme on security grounds while libertarian-minded members, wary of government involvement in Americans' private lives, oppose it.
The Republican National Committee last month approved a resolution to end the surveillance programmes. While some Republicans played down its significance, the nonbinding vote was seen as a nod to Republicans like Paul.
The White House and Justice Department did not comment on the lawsuit specifically, but said they believed the bulk collection of phone records was legal.
"This, we believe, will be a historic lawsuit," Paul said after filing the complaint in US District Court in the District of Columbia. "We believe that this lawsuit could conceivably represent hundreds of millions of people who have phone lines in this country or cellphones."
Ken Cuccinelli, a former attorney general of Virginia, is the suit's lead counsel. Paul appeared at campaign rallies in October to support Cuccinelli's unsuccessful bid for the Virginia governorship. In December, his advisers approached Cuccinelli about participating in the suit.
"This is a constitutional challenge primarily," Cuccinelli said. "We're not debating national security policy."
Cuccinelli has sued the Obama administration before: he was the first state attorney general to mount a legal challenge to the constitutionality of the president's signature health care overhaul.
The bulk collection programme, which is authorised in Section 215 of the USA Patriot Act, sweeps up what is known as metadata for every phone call made in the US.
It collects the number called, the number from which the call is made and the duration and time of the call.