The Telephone Consumer Protection Act of 1991 (TCPA) was passed by the United States Congress and signed into law by President George H. W. Bush as Public Law 102-243, amending the Communications Act of 1934.
"The TCPA is the primary law in the US governing the conduct of telephone solicitations, ie. telemarketing. The TCPA restricts the use of automatic dialing systems, artificial or prerecorded voice messages, SMS text messages received by cell phones, and the use of fax machines to send unsolicited advertisements. It also specifies several technical requirements for fax machines, autodialers, and voice messaging systems -- principally with provisions requiring identification and contact information of the entity using the device to be contained in the message" (Wikipedia article on Telephone Consumer Protection Act of 1991, accessed 10-31-2009).