"How are NSLs different from subpoenas? Are NSLs subject to limitations?"
"NSLs, however, are subject to two significant limitations. First, they are only available for authorized national security investigations (international terrorism or foreign intelligence/counterintelligence investigations), not general criminal investigations or domestic terrorism investigations. Second, unlike administrative subpoenas and grand jury subpoenas, NSLs can only be used to seek certain transactional information permitted under the five NSL provisions, and NSLs cannot be used to acquire the content of any communications."