The act of state doctrine is a court-made (common law) doctrine that prohibits U.S. courts from judging the validity of the official acts of a foreign country that take place within that foreign country's borders.
In New York, as in other U.S. jurisdictions, the act of state doctrine is recognized as a principle of judicial restraint derived from federal common law. This doctrine holds that U.S. courts should not judge the validity of public acts performed by a recognized foreign sovereign within its own territory. The rationale behind this doctrine is to maintain respect for the principle of national sovereignty and to avoid interference with the executive branch's conduct of foreign affairs. While the act of state doctrine is a federal doctrine, New York courts would apply it in cases where it is relevant. However, the doctrine is not absolute and exceptions may apply, such as when a U.S. statute or treaty indicates that certain foreign acts should not be given effect, or when the foreign act violates international law or fundamental policies of the United States.