<blockquote>The decision sets up a potential clash with the United Nations, <a href="http://avalon.law.yale.edu/20th_century/decad036.asp" target="_blank">whose 1947 agreement with the United States</a> governing the body's New York headquarters clearly forbids Washington from prohibiting the entry of U.N. ambassadors.</blockquote>
Via <a href="http://www.foreignpolicy.com/articles/2014/04/11/papers_please">Papers, Please.</a>.
<blockquote>In approving the agreement, Congress added a provision stating that nothing in the text would limit the United States' ability to preserve its national security. That addendum has never been formally accepted by the United Nations, and the United States has rarely invoked the clause. "Up until now, the U.S. has hesitated to use it.</blockquote>