Over 160 countries and the European Union have signed on to the United Nations Convention on the Law of the Sea (Unclos). The United States, however, has long declined to do so.
Now, China has indicated that it might exit the convention if an upcoming ruling by an international tribunal runs counter to its questionable position: that nearly the entire South China Sea is its territory.
The US is urging China to respect the upcoming ruling, which could happen this month and is widely expected to favor the Philippines. In 2013 the Philippines petitioned an international tribunal—the Permanent Court of Arbitration, in The Hague—to rule on whether China’s “nine-dash line” (see below) is valid, under Unclos.
US secretary of defense Ash Carter, speaking at the Shangri-La Dialogue earlier this month, stressed the importance of China respecting the tribunal’s ruling:
The United States views the upcoming ruling by the UN Arbitral Tribunal on the South China Sea as an opportunity for China and the rest of the region to recommit to a principled future, to renewed diplomacy, and to lowering tensions, rather than raising them. All of us should come together to ensure this opportunity is realized.

http://qz.com/712170/china-is-threatening-to-leave-a-major-un-sea-treaty-and-theres-nothing-the-us-can-say-about-it/