The contiguous zone under UNCLOS is the belt of sea between 12 and 24 nautical miles from a coastal state’s baseline where that state may enforce, but not fully govern, a narrow set of its domestic laws. Article 33 of the United Nations Convention on the Law of the Sea limits that authority to four subjects: customs, fiscal, immigration, and sanitary matters.1United Nations. United Nations Convention on the Law of the Sea Foreign vessels keep their freedom of navigation through the zone; the coastal state only gets policing powers tied to what happens, or is about to happen, on its territory or in its territorial sea. As of early 2026, 172 nations are party to UNCLOS, and non-parties such as the United States generally observe these provisions as customary international law.2United Nations. Chronological Lists of Ratifications
What Article 33 Actually Authorizes
Article 33 lets a coastal state “exercise the control necessary” to do two things. First, prevent violations of its customs, fiscal, immigration, or sanitary laws before they occur inside its territory or territorial sea. Second, punish violations of those same laws that have already occurred there. The zone cannot extend beyond 24 nautical miles from the baselines used to measure the territorial sea, so in practice, for states claiming the full 12-mile territorial sea allowed by Article 3, the contiguous zone is the next 12-mile band outward.1United Nations. United Nations Convention on the Law of the Sea
The word “control” was chosen instead of “sovereignty” for a reason. A coastal state cannot regulate fishing, drilling, or scientific research in the contiguous zone on the strength of Article 33. It cannot apply its criminal code broadly to foreign ships passing through. The authority runs in one direction: outward from land, protecting the laws that apply inside the territorial sea. A ship heading toward shore can be stopped if authorities have reasonable grounds to believe it intends to breach one of the four categories. A ship heading away can be stopped if it already has.
Freedom of navigation is preserved. Article 58 confirms that all states enjoy freedoms of navigation and overflight within the exclusive economic zone, which geographically overlaps the contiguous zone.3United Nations. United Nations Convention on the Law of the Sea – Part V Contiguous zone enforcement cannot interfere with innocent passage or with the broader right of transit through these waters.
The Four Enforcement Categories
Customs and Fiscal
This is the most heavily used branch of contiguous zone authority. Coastal nations intercept vessels suspected of smuggling, duty evasion, or moving undeclared cargo toward port. Practical tools include boarding, physical inspection, seizure of contraband, and arrest of crew involved in violations. UNCLOS sets the framework for authority; the actual penalties are set by each state’s own laws.4Office of the Law Revision Counsel. 19 USC 1581 – Boarding Vessels
Immigration
Article 33’s preventive half matters most here. A state does not have to wait for a vessel carrying undocumented passengers to cross into its territorial sea before acting. The contiguous zone gives authorities a legal basis to intercept and turn back vessels involved in unauthorized migration, human trafficking, or attempts to bypass port-of-entry procedures.
Sanitary
Sanitary authority covers quarantine, disease control, and biosecurity. When a ship is suspected of carrying a contagious disease, coastal authorities can require health inspections, restrict movement, or divert the vessel to a designated port for medical clearance. Domestic health regulations flesh out what those measures look like in each country.
Archaeological and Historical Objects
Article 303 adds a fifth category in practical effect. It obliges all states to protect objects of an archaeological and historical nature found at sea, and it authorizes the coastal state to treat the unauthorized removal of such objects from the seabed within the contiguous zone as if it were a violation of the customs, fiscal, immigration, or sanitary laws described in Article 33.5United Nations. United Nations Convention on the Law of the Sea – Part XVI – Article 303 The effect is to push contiguous zone enforcement powers over shipwrecks, artifacts, and other submerged cultural property out to 24 nautical miles.
This is a legal presumption, not an ownership claim over everything on the seabed. Article 303(3) preserves the rights of identifiable owners, the law of salvage, and other admiralty rules. What the coastal state gains is the power to require prior approval for recovery activities and to treat unauthorized removal as a customs-type infringement.
Hot Pursuit From the Zone
Article 111 lets a coastal state chase a foreign vessel onto the high seas if the pursuit begins in the contiguous zone and the vessel is suspected of violating one of the laws the zone protects.6United Nations. United Nations Convention on the Law of the Sea – Part VII Without this rule, a vessel could shake off enforcement simply by crossing into international waters.
The conditions are strict. The pursuing state must give a visual or auditory signal to stop while the foreign vessel is still inside the contiguous zone, and close enough to see or hear it. The pursuit cannot be interrupted: if contact is lost or the chase is broken off, it cannot be resumed. It must end the moment the fleeing ship enters the territorial sea of its own flag state or of any third state.
Pursuit that begins in the contiguous zone is limited to violations of the four Article 33 categories. Suspected illegal fishing would not qualify, because fisheries fall under the exclusive economic zone regime rather than Article 33.
How the Zone Differs From the Territorial Sea and the EEZ
The contiguous zone sits between two other maritime zones, and the differences are what make it a limited enforcement tool rather than a general grant of authority.
In the territorial sea, from the baseline out to 12 nautical miles, the coastal state has full sovereignty over the water, the seabed, and the airspace above, subject only to the right of innocent passage.7United Nations. United Nations Convention on the Law of the Sea – Part II It controls fishing, resource extraction, environmental rules, and criminal law the same way it does on land.
The exclusive economic zone extends up to 200 nautical miles and gives the coastal state sovereign rights over natural resources: fish stocks, oil and gas, and renewable energy from wind and currents.3United Nations. United Nations Convention on the Law of the Sea – Part V Because the contiguous zone sits entirely within the EEZ, both regimes apply in the 12-to-24-mile band at the same time. Enforcing customs law there under Article 33 and enforcing fisheries rules under the EEZ regime are two separate authorities operating in the same water.8National Oceanic and Atmospheric Administration. Maritime Zones and Boundaries
The nature of the authority is what separates them. EEZ rights are economic and cover resources. Contiguous zone powers are administrative and extend domestic regulatory enforcement seaward. Neither approaches the full sovereignty that exists inside the territorial sea.
When Neighboring States Are Too Close for a Full Zone
Where two countries face each other across less than 48 nautical miles of water, their potential contiguous zones overlap. UNCLOS contains no specific delimitation rule for the contiguous zone between adjacent or opposite states. Article 15, which governs the territorial sea, holds that neither state may extend its claim beyond the median line equidistant from each country’s baselines, absent historic title or special circumstances.7United Nations. United Nations Convention on the Law of the Sea – Part II In practice, contiguous zone boundaries tend to follow the same equidistance principle or are set by bilateral agreement.
The U.S. Position Without Ratification
The United States has not ratified UNCLOS but claims a 24-nautical-mile contiguous zone through Presidential Proclamation 7219, issued on September 2, 1999. The proclamation cited law enforcement and public health interests and specifically referred to preventing the unauthorized removal of cultural heritage within 24 nautical miles of the baseline.9The American Presidency Project. Proclamation 7219 – Contiguous Zone of the United States U.S. authorities treat the UNCLOS contiguous zone provisions as reflecting customary international law and enforce them on that basis.