US Republican senator Rand Paul is filing a "class-action" lawsuit challenging a National Security Agency's surveillance program.
Represented by former Virginia attorney general Ken Cuccinelli, Paul filed his suit at 11am (0200 AEDT on Thursday) in the US District Court for the District of Columbia.
Paul's lawsuit is the latest to challenge NSA surveillance, but it's the first to be filed by a member of congress.
It also seeks to distinguish itself as a class-action lawsuit, on behalf of many US residents.
Ultimately, a judge will decide whether to certify the case as a class action or not.
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"I expect this case to go all the way to the Supreme Court, and I predict the American people will win," Paul said.
Various courts have, to date, come to different conclusions about the NSA surveillance program that scoops up bulk telephone and email data.
One federal judge determined last December that the mass data collection was likely to be unconstitutional; another judge, in a different case, concluded otherwise.
The lawsuit names President Barack Obama and several top national security officials as defendants.
Members of congress do not have a great track record in challenging executive actions in court.
Among other hurdles, they must overcome the issue of standing, which includes demonstrating they have suffered actual harm.
There also is a judicial predilection not to interfere with political matters.
In 2011, for instance, then-Representative Democrat Dennis Kucinich and other lawmakers made a brief splash by suing Obama over what they called an "illegal war" against Libya.
Four months later, the case was quietly dismissed.
