Article 9 Vienna Convention on the Law of Treaties
Adoption of the text
1. The adoption of the text of a treaty takes place by the consent of all the States participating in its drawing up except as provided in paragraph 2.
2. The adoption of the text of a treaty at an international conference takes place by the vote of two thirds of the States present and voting, unless by the same majority they shall decide to apply a different rule.
See also: Article 8 Vienna Convention on the Law of Treaties