A case in the International Court of Justice can be brought by one state. The defendant state does not need to be consulted when the case is brought.
However, all state parties must agree and recognise the jurisdiction of the ICJ in a particular matter. This can happen in three ways:
- both parties agree to seek recourse to the Court,
- a clause in a treaty states that disputes will be resolved in the Court
- a state can agree to be bound only in respect of other states that also have agreed to be bound. This is called an "Optional clause declaration".
- Yabulistan and Tokmania both claim the Mago islands. To avoid war they jointly agree to allow the ICJ to consider the legal case.
- Some years ago, Tokmania and Yabulistan signed a treaty which allowed Tokmanian citizens the right to pass through Yabulistan to the Tokmanian enclave of Kingsburgh. In return, Tokmania allows Yabulistan tariff free access to its agricultural markets. The treaty contains a clause which says that any dispute will be resolved by the ICJ. Recently Yabulistan has been requiring Tokmanians to travel on foot. Tokmania believes this is a breach of the treaty and takes Yabulistan to court.
- Yabulistan sees a benefit in binding itself to the ICJ. It passes a law which says that it agrees to be bound by decisions of the ICJ in cases brought by other states that also have agreed to this bind. If Tokmania also passes a similar law (called an "optional law declaration") then Tokmania can bring a case against Yabulistan without a special agreement.
The decisions of the court are binding to the extent that the various nations have agreed to this by joining the UN. Article 94 of the charter provides for the power of the court to make binding decisions. A nation that ignores a decision of the Court could be subject to UN sanctions up to a Security Council authorised military action against that nation.
In the particular case of India and Pakistan. Pakistan has made an optional clause declaration (renewed in 2017), as has India (in 1974). Thus both countries recognise the jurisdiction of the ICJ, with some reservations. However one of the reservations is "disputes with the government of any State which is or has been a Member of the Commonwealth of Nations". A list of the declarations is held by the ICJ