This is the original legislation that Congress passed in 1991. It is 47 U.S.C. § 227 known as the "Telephone Consumer Protection Act or TCPA". Congress mandated that the FCC come up with rules and regulations to limit the industry. The regulations that the FCC came up with became known as C.F.R 64.1200. I have marked some sections in red which pertain to the laws used to take telemarketers to court.

§ 227. Restrictions on use of telephone equipment