The Federal Bureau of Investigation's (FBI) General Counsel, in a Nov. 28, 2001 memo to all FBI field offices, explained the purpose and use of the National Security Letters (NSL) as follows:
"NSLs are administrative subpoenas that can be used to obtain several types of records. There are three types of NSLS. First, pursuant to the Electronic communications Privacy Act (ECPA)..., the FBI can issues NSLS for: (1) telephone subscriber information (limited to name, address, and length of service); (2) telephone local and long distance toll billing records; and (3) electronic communication transactional records. Second, pursuant to the Right to Financial Privacy Act (RFPA)..., the FBI can issue NSLs to obtain financial records from banks and other financial institutions. Finally pursuant to the Fair Credit Reporting Act (FCRA)..., the FBI can issue NSLs to obtain consumer identifying information and the identity of financial institutions from credit bureaus...
[FBI's] Foreign Intelligence Collection and Foreign Counterintelligence investigations (FCIG)... provide that an NSL can be issued during the course of a full international terrorism or foreign counterintelligence investigation. NSLs cannot be used in criminal investigations unrelated to international terrorism or clandestine intelligence activities. [Bold in original text]...
NSLs are powerful investigative tools, in that they can compel the production of substantial amounts of relevant information. However, they must be used judiciously. The USA PATRIOT Act greatly broadened the FBI's authority to gather this information... Executive Order 12333 and the FCIG require that the FBI accomplish its investigations through the 'least intrusive' means... The greater availability of NSLs does not mean that they should be used in every case."
John D. Cline, JD, Attorney, in an Oct. 13, 2004 article titled "Court Strikes Down National Security Letter Statute" published in Jones Day Commentaries wrote that:
"As amended by the USA PATRIOT Act, [Section 2709 of Title 18, United States Code] authorizes the FBI to issue... NSLs based on a certification that the requested documents and information are 'relevant to an authorized investigation to protect against international terrorism or clandestine intelligence activities' and that 'such an investigation of a United States person is not conducted solely on the basis of activities protected by the first amendment to the constitution of the United States.'
The statute does not provide for judicial review of the NSL either before or after issuance. Nor does it include a mechanism for judicial enforcement if the recipient declines to comply with the request.
Section 2709(c) imposes a gag on the recipient of the NSL. The statute declares that '[n]o wire or electronic communication service provider, or officer, employee, or agent thereof, shall disclose to any person that the Federal Bureau of Investigation has sought or obtained access to information or records under this section."
The Congressional Research Service (CRS) Report for Congress, wrote in its Mar. 21, 2006 report titled "National Security Letters in Foreign Intelligence Investigations: A Glimpse of the Legal Background and Recent Amendments," written by Charles Doyle, Senior Specialist, American Law Division:
"Five statutory provisions vest government agencies responsible for certain foreign intelligence investigations (principally the Federal Bureau of Investigation [FBI]) with authority to issue written commands comparable to administrative subpoenas. These National Security Letters (NSLs) seek customer and consumer transaction information in national security investigations from communications providers, financial institutions, and credit agencies. Section 505 of the USA PATRIOT Act expanded the circumstances under which an NSL could be used. Subsequent press accounts suggested that their use had become widespread. Two lower federal courts, however, found the uncertainties, practices, and policies associated with the use of NSL authority contrary to the First Amendment right of freedom of speech, and thus brought into question the extent to which NSL authority could be used in the future. The USA PATRIOT Improvement and Reauthorization Act..., amend the NSL statutes and related law to address some of the concerns raised by critics and the courts."