The Senate approved a five-year extension of a George W. Bush-era surveillance law that allows US spy agencies to conduct wiretapping on foreign citizens without a warrant.
The Foreign Intelligence Surveillance Act, approved by the House of Representatives in September, passed the Senate with a 73-23 vote and broad bipartisan support, and now goes to President Barack Obama for his signature.
Lawmakers shot down three different attempts to add oversight and privacy safeguards to the elements of FISA that authorize the warrantless wiretapping program that was begun under Bush, without congressional authorization, after the September 11, 2001 attacks.
The law allows the collection of intelligence on Americans when they communicate abroad with foreigners designated as potential terror suspects by agencies like the CIA and the National Security Agency.
Some critics have raised concerns that the communications of everyday Americans may be getting swept up in a vast electronic collection of phone calls and emails.
FISA was first passed in 1978 in the aftermath of the Watergate scandal, when lawmakers acted on concerns about the widespread abuse of government wiretaps and the use of intelligence-gathering practices such as eavesdropping.
They inserted safeguards to prevent against unlawful wiretaps of US citizens.
But those safeguards were eased after 9/11 so that intelligence agencies could better track foreign targets, including in 2008 near the end of Bush's second term.
Democratic Senator Ron Wyden introduced an amendment that would require greater disclosure of information about the highly secretive wiretapping program and how it is being used, and said it was vital to institute greater protections against unreasonable violations of US citizens' privacy.
"This is an important time for American security," Wyden said on the Senate floor before his amendment failed to pass.
"It is also an important time for American liberty, and this amendment ensures that we can strike an appropriate balance between protecting our country's well-being and also protecting the individual liberties that we all cherish."
Senator Dianne Feinstein, the Democratic chair of the Senate Intelligence Committee, acknowledged that "there can be some incidental collection of communications who are US persons," such as through a foreign target calling someone in the United States.
"This potential for incidental collection does not mean that the intelligence community is intentionally conducting surveillance on US persons. In fact, doing so would be a violation of law," she added.
In May, Wyden and fellow Democrat Mark Udall wrote the National Security Agency seeking a "ballpark estimate" of how many Americans have been targeted through the FISA Amendments Act of 2008.
The NSA and the inspector general said the request was "beyond the capacity" of their office.
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