Every year, roughly 21 percent of the world's oil and an enormous share of global container traffic passes through the Strait of Hormuz, a 33-mile-wide chokepoint between Iran and Oman. The agency with nominal responsibility for the safety and freedom of that passage is the International Maritime Organization, the United Nations' specialized body for global shipping. This week, the IMO's limits were placed in sharp relief as a de facto dual blockade took shape in the strait for the first time in decades.
What the IMO Is | The UN Body That Sets the Rules of the Sea
The International Maritime Organization was established in 1948 and became operational in 1958. It is the United Nations agency responsible for the safety, security, and environmental performance of international shipping. Its 176 member states adopt binding conventions that govern everything from the construction of vessels to collision-avoidance rules to the rights of seafarers.
The IMO's foundational legal framework for freedom of navigation is UNCLOS, the United Nations Convention on the Law of the Sea, which guarantees the right of innocent passage through international straits. Under UNCLOS, the Strait of Hormuz qualifies as a strait used for international navigation, meaning all vessels have the right of transit passage that cannot be suspended or restricted by the coastal state. In legal terms, Iran cannot legitimately seize foreign-flagged commercial vessels transiting the strait for lacking Iranian-issued permits. The IMO exists, in part, to uphold precisely that principle.
What the IMO lacks is enforcement power. It has no navy. It cannot intercept vessels or compel member states to release seized ships. Its tools are diplomatic, regulatory, and reputational: issuing circulars, convening emergency sessions of the Maritime Safety Committee, and applying collective pressure through member state consensus. When a powerful state decides to ignore those norms, the IMO can document the violation, issue statements, and escalate to the UN Security Council, where geopolitics again take over.
April 22 | Iran Seizes MSC Francesca, Attacks Epaminondas, Fires on Euphoria
On April 22, Iran's Islamic Revolutionary Guard Corps intercepted the Panama-flagged MSC Francesca and the Liberia-flagged Epaminondas, both vessels affiliated with MSC, the world's largest container shipping line. The IRGC stated the ships were seized for transiting without permits, according to Lloyd's List.
Greece's Ministry of Shipping disputed Iran's characterization, telling CNN that the Epaminondas was not seized but was attacked and sustained "extensive damage." A third vessel, the Euphoria, was also fired upon but escaped and continued toward the Gulf of Oman. The distinction between a seizure and an attack matters significantly under IMO conventions: both are violations of innocent passage rights, but an armed attack on a commercial vessel triggers different legal and military response frameworks.
The Dual Blockade | US Navy vs. Iran, Ships Caught in Between
The April 22 seizures did not occur in isolation. Three days earlier, on April 19, the US Navy seized the Iranian-flagged cargo ship Touska for attempting to breach an American blockade of Iranian ports. The action was part of a declared US interdiction campaign targeting Iranian oil exports under maximum pressure sanctions policy.
The combination has produced what analysts describe as a "dual blockade": the US Navy interdicting vessels bound for Iranian ports, while Iran restricts and retaliates against general commercial transit through the strait. This occurred one day after President Donald Trump agreed to extend a ceasefire with Iran, illustrating how the naval dimension of the conflict is operating on a timeline disconnected from diplomatic channels.
For the IMO, a dual blockade scenario is an institutional stress test. Both actions, the US seizure of Touska and Iran's seizure of MSC vessels, represent departures from the freedom of navigation principles the organization is designed to protect. The IMO cannot publicly condemn the United States without fracturing its consensus structure; it cannot ignore Iran's actions without abdicating its mandate.
What Comes Next | IMO Emergency Sessions and Shipping Re-Routing
Major shipping insurers including Lloyd's of London have already elevated the Strait of Hormuz to a designated war risk zone, dramatically increasing insurance premiums for vessels transiting the area. Several carriers have begun re-routing ships around the Cape of Good Hope, adding 10 to 14 days to journey times and increasing fuel costs, a replay of the Red Sea disruption that dominated 2024.
The IMO Maritime Safety Committee can be convened in emergency session at the request of member states. A formal MSC circular documenting the violations is the likely first step, followed by a referral to the UN Secretary-General if seizures continue. The practical question is whether that process moves fast enough to matter when ships are being intercepted in real time.
For more on global shipping disruptions and their economic impact, see ObjectWire Finance. For broader Iran and US foreign policy context, see ObjectWire's Trump administration coverage and ObjectWire Politics.