Commentary: Why freedom of passage through the Strait of Hormuz matters to everyone, not just Singapore

Iran is considered bound by the transit passage regime on the basis that it has become customary international law, having been accepted widely and applied consistently by the rest of the world. However, Iran has argued that it is not bound as the transit passage regime is not customary international law. Iran has persistently objected to the transit passage regime.

Notwithstanding this disagreement, Iran is in any event bound by the customary international law principle pre-dating UNCLOS that strait states cannot prohibit, hamper or suspend innocent passage of ships through straits used for international navigation.

Because Iran, Israel and the United States are at war, it also triggers a separate, older law of naval warfare. It affirms that the peacetime right of transit passage under UNCLOS does not disappear in armed conflict. 

Countries not involved in the fighting – neutral states – retain the right to move their commercial ships through the strait. Those engaged in the armed conflict – belligerent states – may restrict enemy vessels belonging to each other or ships actively assisting the enemy.