Article 54 Vienna Convention on the Law of Treaties
Termination of or withdrawal from a treaty under its provisions or by consent of the parties
The termination of a treaty or the withdrawal of a party may take place:
(a) in conformity with the provisions of the treaty; or
(b) at any time by consent of all the parties after consultation with the other contracting States.
See also: Article 53 Vienna Convention on the Law of Treaties