From the website: "In October 1994, Congress took action to protect public safety and ensure national security by enacting the Communications Assistance for Law Enforcement Act of 1994 (CALEA ), Pub. L. [Public Law] No. 103-414, 108 Stat. [Statute] 4279. The law further defines the existing statutory obligation of telecommunications carriers to assist law enforcement in executing electronic surveillance pursuant to court order or other lawful authorization. The objective of CALEA implementation is to preserve law enforcement's ability to conduct lawfully-authorized electronic surveillance while preserving public safety, the public's right to privacy, and the telecommunications industry's competitiveness."
Ask CALEA: http://www.askcalea.fbi.gov/