General Discussion

Google says: The instruction to interdict foreign merchant vessels in international waters for paying "tolls" to Iran is a significant escalation that conflicts with established international law and faces legal challenges under domestic U.S. law.

Interdicting foreign vessels on the high seas is generally considered illegal under international law unless specific, narrow exceptions are met.

Freedom of Navigation: International waters are governed by the principle that no single country has jurisdiction over foreign vessels. Article 94 of the UN Convention on the Law of the Sea (UNCLOS) and the 1958 Convention on the High Seas prohibit such interdictions without the consent of the vessel’s "flag state" (the country where it is registered).

Permissible Exceptions: Interdiction is only legal in cases of piracy, slave trading, unauthorized broadcasting, or if a vessel is stateless. Paying a toll to another nation does not fall under these categories.
Lack of Multilateral Support: Since these sanctions are typically unilateral U.S. measures rather than UN Security Council mandates, they do not have the global binding authority required to bypass sovereign immunity on the high seas.

While a President has broad authority to enforce sanctions through the International Emergency Economic Powers Act (IEEPA), this authority is primarily domestic.

Statutory Limits: IEEPA allows the U.S. to block property and financial transactions within U.S. jurisdiction, but it does not explicitly grant the power to seize foreign ships in international waters purely for violating U.S. economic policy.

Constitutional Questions: Aggressive high-seas seizures may be challenged in U.S. courts as exceeding executive authority or violating due process, especially if the seizures occur without a specific domestic warrant or statutory basis for international enforcement.

Context of the Instruction
This directive was issued by President Donald Trump on April 12, 2026, following the collapse of ceasefire negotiations with Iran in Islamabad.

The "Toll" Issue: The order responds to Iran's attempts to charge vessels for passage through the Strait of Hormuz, which Trump characterized as "illegal extortion".
Blockade Status: In addition to interdiction, the President declared a naval blockade of the Strait—an action that is traditionally defined as an act of war under international law.