To address the nation's critical organ donation shortage and improve the organ matching and placement process, the U.S. Congress passed the National Organ Transplant Act* (NOTA) in 1984. The act established the Organ Procurement and Transplantation Network (OPTN) to maintain a national registry for organ matching. The act also called for the network to be operated by a private, non-profit organization under federal contract.
The current U.S. Code that has resulted from NOTA and its amendments can be found here: http://uscode.house.gov/search/criteria.shtml. Search for Title 42, Section 273.