Article IV, Section 2, Clause 3:
No Person held to Service or Labour in one State, under the Laws thereof, escaping into another, shall, in Consequence of any Law or Regulation therein, be discharged from such Service or Labour, but shall be delivered up on Claim of the Party to whom such Service or Labour may be due.
This clause contemplated the existence of a positive unqualified right on the part of the owner of a slave which no state law could in any way regulate, control, or restrain. Consequently the owner of a slave had the same right to seize and repossess him in another state, as the local laws of his own state conferred upon him, and a state law that penalized such seizure was held unconstitutional. 1 Congress had the power and the duty, which it exercised by the Act of February 12, 1793, 2 to carry into effect the rights given by this section, 3 and the states had no concurrent power to legislate on the subject. 4 However, a state statute providing a penalty for harboring a fugitive slave was held not to conflict with this clause because it did not affect the right or remedy either of the master or the slave; by it the state simply prescribed a rule of conduct for its own citizens in the exercise of its police power. 5