Republican presidential candidate Rand Paul has commandeered the Senate floor to deliver a nearly 11 hours-long protest against the renewal of the US Patriot Act, which allows the spy agencies' collection of Americans' telephone data.
Under Senate rules, Paul, was able to stay on the Senate floor and speak without interruption until midnight, when the next legislative day begins.
"There is a general veil of suspicion that is placed on every American now. Every American is somehow said to be under suspicion because we are collecting the records of every American," Paul said on Wednesday.
He finished at 11:49 pm local time, having not sat for more than 10 hours.
Rand trended on Twitter during the filibuster by asking people to take selfies of themselves watching him on the Senate floor and adding the hashtag #StandwithRand.
Although both chambers are controlled by Republicans, leaders of the House of Representatives and Senate have been unable to agree on how to prevent the expiration of provisions of the act that provide the legal basis for the collection of billions of telephone call records and other business information.
The House of Representatives has already passed legislation, the USA Freedom Act, that would limit agencies' ability to collect Americans' electronic data and business records.
That measure would end bulk data collection but replaces it with a system of targeted information retrieval.
The programme has been a deep concern for privacy advocates since it was exposed two years ago by former National Security Agency contractor Edward Snowden, who is now a fugitive in Russia.
There is strong support among Republicans and Democrats for extensive reform of the programme, but few want it to expire.
US intelligence officials insist it is necessary to protect Americans.
President Barack Obama has said he would sign the legislation if it is passed in the Senate.
Paul is leading the opposition to an extension of the measure, saying he would block even a two- or three-day extension.