( CNN ) -- By a substantial margin , the Senate on Friday passed an extension of a controversial overseas wiretapping program , the Foreign Intelligence Surveillance Act . The law has already been reauthorized by the House , and President Obama is expected to sign it . According to Sen. Dianne Feinstein , D-California , who is chairman of the Senate Intelligence Committee , the law , know by its acronynm FISA , has helped authorities prevent terrorist plots . `` In the past four years , there have been one hundred arrests to prevent something from happening in the United States , '' Feinstein said . `` Some of these plots have been thwarted because of this program . I think it is a vital program . '' But critics say the law gives intelligence agencies wide latitude in carrying out surveillance , under oversight by a special FISA court whose proceedings are not public . `` It 's something with enormous potential for abuse , '' said Julian Sanchez , with the libertarian Cato Institute . `` The FISA Amendments Act authorizes what the Fourth Amendment was written to prevent , which is to say , general warrants -- blank checks for surveillance . '' In 2005 , a national debate erupted when the Terrorist Surveillance Program authorized by President George W. Bush was revealed in the media . Under that program , begun shortly after the 9/11 attacks , intelligence agencies could spy on communications between U.S. residents and people overseas without a warrant , if it was believed one of the parties was linked to terrorism . The FISA law passed in 2008 required officials to obtain a warrant to spy on any American -- including , for the first time , Americans who are abroad . The law also established FISA as the exclusive means for authorizing electronic surveillance . Privacy advocates say if a foreigner overseas is being wiretapped , which does not require a warrant , an American communicating with that person could still have their communications with that foreigner monitored . But defenders say the law contains provisions to protect privacy and prevent abuse , including a prohibition on spying on Americans except with a warrant . The National Security Agency , the country 's primary surveillance agency , told CNN in a statement : `` One of the biggest misconceptions about NSA is that we are unlawfully listening in on , or reading e-mails of , U.S. citizens . This is simply not the case . NSA is unwavering in its respect for U.S. laws and Americans ' civil liberties . '' Sen. Ron Wyden , D-Oregon , proposed an amendment requiring more disclosure . `` I think we ought to know , generally , how many Americans are being swept up under the legislation , '' he said during Thursday 's debate on the Senate floor . But defenders of the law say , the effectiveness of espionage programs depends on a level of secrecy . `` It 's very hard to have covert and clandestine intelligence-gathering , if it 's not secret , '' said Clifford May , an advocate of national security with the Foundation for Defense of Democracies . Without reauthorization , the law was scheduled to expire Monday , at the end of 2012 .
The law has helped authorities prevent terrorist plots , says a senator . But `` It 's something with enormous potential for abuse , '' says a member of Cato Institute . The law , passed in 2008 , requires officials to obtain a warrant to spy on any American . Opponents say Americans communicating with persons abroad still could be spied on .