Article 22 Vienna Convention on the Law of Treaties

Withdrawal of reservations and of objections to reservations

1. Unless the treaty otherwise provides, a reservation may be withdrawn at any time and the
   consent of a State which has accepted the reservation is not required for its withdrawal.
2. Unless the treaty otherwise provides, an objection to a reservation may be withdrawn at any
   time.
3. Unless the treaty otherwise provides, or it is otherwise agreed:

(a) the withdrawal of a reservation becomes operative in relation to another contracting State only when notice of it has been received by that State;

(b) the withdrawal of an objection to a reservation becomes operative only when notice of it has been
received by the State which formulated the reservation.

See also: Article 21 Vienna Convention on the Law of Treaties