NSL meaning in Military and Defence ?

A national security letter (NSL) is an administrative subpoena issued by the United States government to gather information for national security purposes. NSLs do not require prior approval from a judge. The Stored Communications Act, Fair Credit Reporting Act, and Right to Financial Privacy Act authorize the United States government to seek such information that is "relevant" to authorized national security investigations. By law, NSLs can request only non-content information, for example, transactional records and phone numbers dialed, but never the content of telephone calls or e-mails.

NSLs typically contain a nondisclosure requirement forbidding the recipient of an NSL from disclosing that the FBI had requested the information. The nondisclosure provision must be authorized by the Director of the FBI, and only after he or she certifies "that otherwise there may result a danger to the national security of the United States; interference with a criminal, counterterrorism, or counterintelligence investigation; interference with diplomatic relations; or danger to the life or physical safety of any person." Moreover, a recipient of the NSL may still challenge the nondisclosure provision in federal court.

The constitutionality of such nondisclosure provisions has been repeatedly challenged. The nondisclosure provision was initially ruled unconstitutional as an infringement of free speech in Doe v. Gonzales, but that decision was later vacated in 2008 by the Second Circuit Court of Appeals after the court held the USA PATRIOT Improvement and Reauthorization Act gave the recipient of an NSL that included a nondisclosure provision the right to challenge the nondisclosure provision in federal court. In March 2013, a federal judge in the Northern District of California held the nondisclosure provision in an NSL was unconstitutional. On August 24, 2015, the Ninth Circuit Court of Appeals vacated the court's decision and remanded the case for further proceedings. On remand, the district court held the "NSLs were issued in full compliance with the procedural and substantive requirements suggested by the Second Circuit in John Doe, Inc. v. Mukasey, 549 F.3d 861 (2d Cir. 2008), which had held that the 2006 NSL law could be constitutionally applied"... and "the NSL law, as amended [by the USA FREEDOM ACT of 2015], was constitutional." The two petitioners appealed. On appeal, the Ninth Circuit Court of Appeals upheld the district court ruling, holding that NSLs are constitutional, holding "the nondisclosure requirement does not run afoul of the First Amendment." Under Seal v. Jefferson B. Sessions, III, Attorney General, Nos. 16-16067, 16-16081, and 16-16082, July 17, 2017.