"Treat references to legal materials like reference to works with no author; that is, in text, cite materials such as court cases, statutes, and legislation by the first few words of the reference and the year..." (Publication Manual of the American Psychological Association, 2010, p. 177]
Unlike APA style for other materials, however, legal and legislative citations make heavy use of standard abbreviations and document numbering systems: "Follow the Bluebook closely for correct abbreviation style." (Publication Manual of the American Psychological Association, 2010, p. 216)
As noted above, the APA directs users to The Bluebook for guidance on legal citation style:
"The Bluebook requires the use and citation of traditional printed sources when available, unless there is a digital copy of the source available that is authenticated, official, or an exact copy of the printed source
....When an authenticated, official, or exact copy of a source is available online, citation can be made as if to the original print source (without any URL information appended.)
"Where a print version is accessible, citation should be made to the print source." (Bluebook, p. 131)* If citing to an electronic source, "All efforts should be made to cite to the most stable electronic location available." (Bluebook, p.171)
Examples of stable, electronic sources for legislative and legal documents include FDSys (the Government Printing Office digital system), Proquest Congressional, LexisNexis Academic, Hein Online, and the Congressional Serial Set Online.
A librarian can help you to locate the document in a stable, electronic or print source. When in doubt, Ask a Librarian!