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 Pennsylvania, 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, Pennsylvania courts will apply it as directed by the U.S. Supreme Court and relevant federal case law when dealing with cases that involve foreign governmental acts. It is important to note that there are exceptions to this doctrine, such as when a U.S. statute or treaty explicitly allows for judicial review of foreign acts, or when the foreign state has waived its immunity.