In The United States v. Ephraim Briggs, the Supreme Court was asked to decide whether a federal statute that prohibited the importation of slaves into any port or place within the jurisdiction of the United States applied to persons who had been brought from abroad and were then found in a state not under federal control. The court held that it did apply, finding that Congress had authority over all places where its laws could be enforced by appropriate means. In addition, they determined that even though slavery was legal in some states at this time, it did not give individuals immunity from prosecution for violating national law prohibiting slave trading. This decision established an important precedent regarding Congressional power over interstate commerce and affirmed Congress' ability to regulate activities related to slavery throughout US territories regardless of local laws on the matter.

In the United States v. Ephraim Briggs, Justice McLean dissented from the majority opinion of the Court. He argued that Congress had no authority to pass a law prohibiting slavery in any territory acquired by treaty with foreign nations, as was done in this case. He further stated that even if such a law were constitutional, it would be void because it violated Article IV of the Constitution which states that “the citizens of each state shall be entitled to all privileges and immunities of citizens in the several states” and thus could not deny slaves their rights as property owners without due process or compensation for their losses. Finally, he noted that while Congress has broad powers over territories under its control, those powers are limited by other provisions within the Constitution and cannot infringe upon individual rights granted therein.