The Treaty of Organia (also known as the Organia Peace Treaty) was a peace treaty forced on the United Federation of Planets and Klingon Empire by the Organians to bring an end to the Federation-Klingon War in 2267. (TOS: "Errand of Mercy")
Article 7 of the Organian Treaty grants free travel to neutral worlds within a territory on the grounds of commerce, diplomacy, or aid.
*Article 7 was invoked by the Klingon Empire in 2271 in granting them unimpeded access to Son'a territory though the territory of United Federation of Planets. (Star Trek Online: The Battle of Klach D'kel Brakt) Edit
Article 366 of the Organian Accords were a clause by which a vessel could enter the Klingon Neutral Zone to rapidly extract a damaged vessel without that action being considered an act of war. (Star Trek: Avenger: "Tales of the Kobayashi Maru: Rahadyan's Story")