Under FISA (Foreign Intelligence Surveillance Act) there are provisions for not needing a court order/warrant for up to a year when dealing with foreign governments and terrorists. There are many related requirements including the notification of the House and Senate Intelligence leaders. It can be found at United States Code Title 50, Chapter 36. http://www.law.cornell.edu/uscode/html/uscode50/usc_sup_01_50_10_36.html