The Northern Sea Route (NSR) for the Russian Federation is a strategically important maritime communication with the status of a historically established national transport artery. Despite its applicability to the Arctic, and therefore to the waters of the NSR, the norms and provisions of the modern international maritime law, and, first of all, the UN Convention on the Law of the Sea 1982 (UNCLOS), Russia declares the important role of the national legislation on the regulation of navigation on the NSR. Such a situation is conditioned by the existing historical practice, the tacit consent of most states, as well as the special environmental vulnerability of the Arctic region and the desire to prevent the marine environment pollution due to the navigation. Among the main opponents of this approach is the USA, which traditionally disputes the unified permitting regime for navigation along the NSR as an example of Russia's extremely broad interpretation of the norms and provisions of UNCLOS. The first part of the paper will show how those legal approaches used by Russia to introduce the national level of the NSR regulation, i.e., the concept of internal historical waters and the method of straight baselines, do not contradict UNCLOS, as they go beyond its limits and are based mostly on customary norms of international law (the so-called international custom) rather than treaties. The U.S. disagreement with such an assertion is discredited by the fact that Washington is not a full party to UNCLOS, and thus cannot fully enjoy all the prerogatives it has introduced.