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 Massachusetts, as in other U.S. states, the act of state doctrine is recognized and applied based on federal common law principles rather than state statutes. This doctrine holds that U.S. courts will generally refrain from evaluating the legality of governmental actions taken by a foreign sovereign within its own territory. The rationale behind this doctrine is to respect the sovereignty of foreign nations and to avoid conflicts in foreign relations that could arise from the judicial assessment of such actions. While the act of state doctrine is a federal doctrine, its application can be relevant in state courts when they are dealing with cases that involve questions about the validity of foreign sovereign acts. However, there are exceptions to the doctrine, such as when a U.S. statute or treaty explicitly indicates that certain foreign acts may be subject to judicial scrutiny, or when the foreign act violates international law or fundamental human rights.