Consistent practice of states illustrates that UNCLOS freedom of navigation provisions have become customary international law

One way to determine the extent to which UNCLOS’s navigational provisions have achieved the status of binding international law is to study the behavior of nations. Behavior in conformity with the convention—known as “state practice”—is additional evidence that its navigational provisions reflect international law. Indications that a state is acting in conformity with international law may be found in states’ “legislation, the decisions of their courts, and the statements of their official government and diplomatic representatives.” A nation’s inaction regarding a particular navigational provision may also be viewed as state practice because it can be deemed to be acquiescence. The consistent practice of states—maritime states, coastal states, UNCLOS members, and nonmembers—indicates that the UNCLOS navigational provisions are almost universally accepted law. The Restatement of the Law, Third, of the Foreign Relations Law of the United States notes:

[B]y express or tacit agreement accompanied by consistent practice, the United States, and states generally, have accepted the substantive provisions of the Convention, other than those addressing deep sea-bed mining, as statements of customary law binding upon them apart from the Convention.