Mason v. United States was a Supreme Court case in which the Court held that the United States had the right to tax the income of a foreign corporation. The case arose when the United States attempted to tax the income of a British corporation, Mason & Co., which had been doing business in the United States. Mason & Co. argued that the United States did not have the right to tax its income because it was a foreign corporation. The Supreme Court disagreed, holding that the United States had the right to tax the income of foreign corporations doing business in the United States. The Court reasoned that the United States had the right to tax the income of foreign corporations because it had the right to regulate the activities of foreign corporations within its borders. The Court also held that the United States had the right to tax the income of foreign corporations because it had the right to protect its citizens from unfair competition. The Court's decision in Mason v. United States established the principle that the United States has the right to tax the income of foreign corporations doing business in the United States.

In Mason v. United States, the Supreme Court was asked to decide whether a person who had been convicted of an offense in one state and then moved to another state could be extradited back to the first state for punishment. The majority opinion held that such extradition was permissible under federal law, but Justice Field dissented from this decision. He argued that Congress did not have the power under Article IV of the Constitution to pass laws allowing extradition between states because it would interfere with each state's sovereignty over its own criminal justice system. Furthermore, he contended that if Congress were allowed to do so, it would lead to unequal treatment of citizens depending on which state they lived in since some states might refuse extradition while others may grant it more readily. Finally, he noted that there was no precedent for such a practice prior to this case and thus urged caution before allowing interstate extraditions without further consideration by Congress or other legal authorities.