Article 62 Vienna Convention on the Law of Treaties
Fundamental change of circumstances
1. A fundamental change of circumstances which has occurred with regard to those existing at the time of the conclusion of a treaty, and which was not foreseen by the parties, may not be invoked as a ground for terminating or withdrawing from the treaty unless:
(a) the existence of those circumstances constituted an essential basis of the consent of the parties to
be bound by the treaty; and
(b) the effect of the change is radically to transform the extent of obligations still to be performed
under the treaty.
2. A fundamental change of circumstances may not be invoked as a ground for terminating or withdrawing from a treaty:
(a) if the treaty establishes a boundary; or
(b) if the fundamental change is the result of a breach by the party invoking it either of an obligation under the treaty or of any other international obligation owed to any other party to the treaty.
3. If, under the foregoing paragraphs, a party may invoke a fundamental change of circumstances as a ground for terminating or withdrawing from a treaty it may also invoke the change as a ground for suspending the operation of the treaty.
See also: Article 61 Vienna Convention on the Law of Treaties