Framework of UNCLOS has become binding on even non-signatory states

Finally, the "other" law of the sea, like UNCLOS, consists of treaties that are notionally binding only on signatory states. Thus, theoretically, nonsignatory nations do not have to comply with their standards, and coastal/port states cannot formally utilize the specific provisions of these treaties when taking, or anticipating the need to take, control actions aboard vessels of nonsignatory states. But the reality is that the vast majority of nations in general, and flag states in particular, have adopted them. A very few vessels flagged by nonsignatory states do engage in international trade; it can certainly be argued, however, that many of the provisions of the supplementary instruments are so widely adhered to that they have acquired the status of customary international law, binding for those states too, if they have not expressly "opted out." This argument, coupled with UNCLOS's grant of authority to port/coastal states to ensure foreign vessel adherence to "other rules of international law" and "generally accepted international rules or standards," gives such states significant clout over vessels flagged by states that have not specifically adopted those rules and standards.43