Article 20 Vienna Convention on the Law of Treaties

Acceptance of and objection to reservations

1. A reservation expressly authorized by a treaty does not require any subsequent acceptance by
   the other contracting States unless the treaty so provides.
2. When it appears from the limited number of the negotiating States and the object and purpose of
   a treaty that the application of the treaty in its entirety between all the parties is an essential condition of
   the consent of each one to be bound by the treaty, a reservation requires acceptance by all the parties.
3. When a treaty is a constituent instrument of an international organization and unless it
   otherwise provides, a reservation requires the acceptance of the competent organ of that organization.
4. In cases not falling under the preceding paragraphs and unless the treaty otherwise provides:

(a) acceptance by another contracting State of a reservation constitutes the reserving State a party to
the treaty in relation to that other State if or when the treaty is in force for those States;
(b) an objection by another contracting State to a reservation does not preclude the entry into force of
the treaty as between the objecting and reserving States unless a contrary intention is definitely
expressed by the objecting State;
(c) an act expressing a State’s consent to be bound by the treaty and containing a reservation is
effective as soon as at least one other contracting State has accepted the reservation.

5. For the purposes of paragraphs 2 and 4 and unless the treaty otherwise provides, a reservation is
   considered to have been accepted by a State if it shall have raised no objection to the reservation by the
   end of a period of twelve months after it was notified of the reservation or by the date on which it
   expressed its consent to be bound by the treaty, whichever is later.

See also: Article 19 Vienna Convention on the Law of Treaties