Would it Be Illegal for Iran to Close the Strait of Hormuz?
In response to international economic and diplomatic pressure to halt its nuclear program, Iran is reportedly contemplating closing the Strait of Hormuz, a narrow and critically important waterway through which approximately a third of global sea-based oil shipments pass each year. The precise nature of this potential action is a little unclear from media reports. Some accounts state that the closure would pertain only to foreign warships that do not receive Iranian permission to transit. Others give the impression that Iran may bar all transit, including oil shipments. The difference is significant, but many seem to think that Iran would be acting illegally either way. My aim here is to briefly explore that view under international law.
The principal hurdle to either type of closure is the U.N. Convention on the Law of the Sea, a treaty that Iran has not ratified but that is widely accepted as codifying preexisting customary rules that bind parties and non-parties alike. One such rule is that in a strait all ships and aircraft shall enjoy an unimpeded right of “transit passage,” which is “the exercise . . . of the freedom of navigation and overflight solely for the purpose of continuous and expeditious transit of the strait” (art. 38). A corollary is that states bordering straits “shall not hamper transit passage,” and that “[t]here shall be no suspension of transit passage” (art. 44).