The mail cover surveillance requests are granted for about 30 days, and can be extended for up to 120 days. There are two kinds of mail covers: those related to criminal activity and those requested to protect national security. Criminal activity requests average 15,000 to 20,000 per year, said law enforcement officials, who spoke on the condition of anonymity because they are prohibited by law from discussing them. The number of requests for antiterrorism mail covers has not been made public.
Law enforcement officials need warrants to open the mail, although President George W. Bush asserted in a signing statement in 2007 that the federal government had the authority to open mail without warrants in emergencies or in foreign intelligence cases.
Court challenges to mail covers have generally failed because judges have ruled that there is no reasonable expectation of privacy for information contained on the outside of a letter. Officials in both the Bush and Obama administrations, in fact, have used the mail-cover court rulings to justify the N.S.A.’s surveillance programs, saying the electronic monitoring amounts to the same thing as a mail cover. Congress briefly conducted hearings on mail cover programs in 1976, but has not revisited the issue.
