US already accepts UNCLOS rules in Proliferation Security Initiative but doesn't have ability to guide its development as non-party

Moreover, current U.S. nonproliferation policy relies on the Convention. The Proliferation Security Initiative, an effort among more than 20 states, led by the United States, to share intelligence and stop weapons shipments, must conform to the Law of the Sea Convention. The other states in the PSI are party to the Convention.13 In their Statement of Interdiction Principles, the PSI parties agree to adhere to international law.14 In effect, this agreement means that when the United States works with allies as part of the PSI, it agrees to observe the rights of innocent passage and freedom of the seas. This agreement costs America nothing, because it already recognizes those rights. The United States could, of course, forcibly violate established rights of free passage in order to interdict weapons shipments. But this policy would be disastrous for two reasons. First, it would undermine the right of free passage, which is essential to U.S. trade and force projection. Second, it would destroy the Proliferation Security Initiative. The PSI cannot work without the cooperation of our allies, and their cooperation depends on the Initiative’s adherence to the Law of the Sea. Instead of fighting proliferation outside of international law, America can use international law to fight proliferation. One way to allow interdiction of weapons shipments is to alter the Convention to make proliferation grounds for interdiction on the high seas or in coastal waters. It would take a long negotiating effort, but the United States might succeed. By staying outside the Convention, the United States forgoes this opportunity but remains bound by the legal restrictions on interdiction.