For the first time in nearly four decades, a senior intelligence official - not a secretive federal court - will have a decisive voice in whether Americans' communications can be monitored when they talk to foreigners overseas.
The shift came over the weekend as Congress hustled through changes to the 1978 Foreign Intelligence Surveillance Act, known as FISA.
The bill provides new powers to the National Security Agency to monitor communications that enter the United States and involve foreigners who are the subjects of a national security investigation.
Apprehensive about what they were doing, Congress specified that the new provisions would expire after six months, unless renewed. They give national intelligence director Mike McConnell and Attorney General Alberto Gonzales joint authority to approve monitoring such calls and e-mails, rather than the 11-member Foreign Intelligence Surveillance Court.
Civil liberties groups and some Democrats call the bill a vast expansion of government power. Officials who work for McConnell, the Justice Department and the Republican congressional leadership have argued that that isn't so.
However, the law's wording - underscored by conversations with Bush administration officials - shows the rules governing when and how Americans' calls and e-mails will be monitored have changed significantly.
Communications that can get caught up in intelligence collection require a spectrum of approvals, depending on the circumstances. Generally, such phone calls, e-mails, text messages and other electronic exchanges fall into three categories.
Purely foreign overseas communications: The National Security Agency can monitor these calls and e-mails without any signoff from a judge or a senior government official.
Domestic conversations between two Americans: The Fourth Amendment's protection against unreasonable search and seizure requires that the government get approval from a court before eavesdropping on these exchanges.
Communications between an American and a foreigner: This is a more complex area. If the American is the target of the investigation, then a court must approve the surveillance, the White House says. However, if the foreigner is the target, no court approval is necessary under the new law. Instead, the attorney general and the national intelligence director will decide together whether to go ahead with the work.