U.S. reliance on customary international law to secure rights is "less certain, more risky, and more costly"
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If it ratifies UNCLOS, the United States seeks to gain “maximum freedom to navigate and operate off foreign coasts without interference,” for both security and economic purposes.87 If the United States does not ratify UNCLOS, it may attempt to assert these freedoms under customary international law. However, its ability to do so is growing weaker, as when coastal States extend their exclusive economic zones, “customary international law may . . . evolve in a way contrary to [American] [i]nterests.”88 Customary law is “not universally accepted, evolves based on State practice, and does not provide access to the Convention’s procedural mechanisms, such as the continental shelf commission.”89 The United States may make excessive maritime claims through customary international law or military operations, but either such approach is “less certain, more risky, and more costly” than working under the UNCLOS framework.90
Opponents of UNCLOS claim that the United States should not become a party because the United States already enjoys the benefits of UNCLOS through customary law and, therefore, should not unnecessarily incur the treaty's burdens. However, this ignores the fact that customary law can change and can also be influenced by how parties to UNCLOS decide to interpret its provisions.