National Security Letters in Foreign Intelligence Investigations: A Glimpse at the Legal Background, Charles Doyle, Senior Specialist in American Public Law. July 31, 2015.

“Five federal statutes authorize intelligence officials to request certain business record information in connection with national security investigations. The authority to issue these national security letters (NSLs) is comparable to the authority to issue administrative subpoenas. The USA PATRIOT Act (P.L. 107-56) expanded the authority under the original four NSL statutes and created a fifth. Thereafter, the authority was reported to have been widely used. Then, a report by the Department of Justice’s Inspector General (IG) found that in its use of expanded USA PATRIOT Act authority the FBI had “used NSLs in violation of applicable NSL statutes, Attorney General Guidelines, and internal FBI policies,” although it concluded that no criminal laws had been broken. A year later, a second IG report confirmed the findings of the first, and noted the corrective measures taken in response. A third IG report, critical of the FBI’s use of exigent letters and informal NSL alternatives, noted that the practice had been stopped and related problems addressed.”