Federal Wiretap Act (see 18 U.S.C. §2511(2)(a)(i))
The overriding limitation to activities in the law enforcement area is the Fourth Amendment to the U.S. Constitution. Thus, law enforcement agents must generally obtain court authorization whenever their activities would contravene one’s reasonable expectation of privacy. In fact, however, it is additional statutory layers of protection that Congress has added over the years that have caused the most difficulty. Indeed, until the passage of the USA PATRIOT Act, many argued that law enforcement agents could not legally monitor an illegal intruder on a Government computer, without the hacker’s consent or a court order.