The Vienna Convention on the Law of Treaties has provisions with regards to action a state may take in response to a reservation to a treaty. Assume that Article 20 (1-3) do not apply.
A reservation established with regard to another party in accordance with articles 19, 20 and 23:
(a) modifies for the reserving State in its relations with that other party the provisions of the treaty to which the reservation relates to the extent of the reservation; and
(b) modifies those provisions to the same extent for that other party in its relations with the reserving State.
The reservation does not modify the provisions of the treaty for the other parties to the treaty inter se.
When a State objecting to a reservation has not opposed the entry into force of the treaty between itself and the reserving State, the provisions to which the reservation relates do not apply as between the two States to the extent of the reservation.