National Security Letter Law and Legal Definition

National security letters are administrative orders that are sent to compel the recipients of the letters to provide information to federal investigators. As authorized by the U.S. Patriot Act, the letters includes gag orders that forbid recipients from discussing the letter's contents and instructions. The letters do not require a judge's authorization, and are subject to limited judicial review. These letters are used by the Federal Bureau of Investigation, and possibly other federal agencies.