The Prize Cases (1863) were a set of cases argued in front of the United States Supreme Court beginning in February 1863. The argument being whether or not the blockaded of Southern ports as ordered by President Abraham Lincoln was constitutionally sound.
The Union’s blockade of Confederate held ports resulted in the seizure of many ships both American and foreign held. Any ship caught while trying run the blockade or smuggle good in or out of the blocked ports where seized. The question before the court was whether or not these ships where captured as a part of war and therefore could be kept as a prize, or if they had been pirated. The United States Supreme Court looked to international law for answers. The opinion of the majority was written by Justice Robert Cooper Grier on March 10th 1863 and concluded that "it is not necessary to constitute war, that both parties should be acknowledged as independent nations or sovereign States." It said the President as Commander-in-chief has the authority to declare a blockade and did not need Congressional approval.
If you’re interested in more information about this topic History 404: US Constitution Seminar i
s good place to start.