President Bush authorized a surveillance program in late 2001, allowing the NSA to monitor communications between the United States and foreign countries without court oversight when a party is believed to be linked to al-Qaeda. Administration officials have recently acknowledged that the NSA program was broader, and intelligence sources have described a vast effort to collect and analyze telephone and e-mail communications that were later scrutinized by the government for desired information. There have been fierce disagreements about the program's legality. Critics say the agency's eavesdropping activities violate the 1978 Foreign Intelligence Surveillance Act (FISA), when "there is probable cause to believe" that one of the parties is a member of a terrorist group.
Revelations in May 2006 showed that the NSA made an effort to log a majority of the telephone calls made within the United States since Sept. 11, 2001 -- amassing the domestic call records of tens of millions of U.S. households and businesses in an attempt to sift them for clues about terrorist threats.