Under international law, the construction of artificial islands confers no right of sovereignty over neighboring waters, and the United States has made it clear that it will not respect China’s claim to what it sees as international waters and airspace.
http://www.washingtonpost.com/world/asia_pacific/chinese-warnings-to-us-plane-hint-of-rising-stakes-over-disputed-islands/2015/05/21/381fffd6-8671-420b-b863-57d092ccac2d_story.html