When the author is an organization versus an individual, completely spell out the name of the entity in your signal phrase -- this is the preferred use -- or in the parenthetical citation the first time you cite the source. When an entity has a widely know abbreviation, place it in brackets directly after the name so that you can use the abbreviation alone in subsequent citations. For example:
"The National Association for the Advancement of Colored People [NAACP] seeks to . . . (n.d.)."
Subsequent signal phrase citations would read: "The NAACP refuted . . ." List subsequent parenthetical citations as: (NAACP). Do not repeat the date or "n.d" -- which stands for no date -- for the same composition by the same author in later citations.
The References page entry includes the name of the organization in full, the date or "n.d." in parenthesis, the title of the Web page in sentence case, the most recent date of access following the word "Retrieved" and the URL address with no ending period. For example:
National Association for the Advancement of Colored People. (n.d.). Our mission. Retrieved June 4, 2013, from http://www.naacp.org/pages/our-mission.