Compact Clause Law and Legal Definition

Compact Clause is a provision in Article I, Section 10, Clause 3, of the U.S. Constitution. Under the Compact Clause, states may not lay any duty of tonnage; keep troops or armies during times of peace without the consent of Congress. They shall not enter into alliances nor compacts or agreements with foreign states, nor engage in war unless invaded or faced with imminent danger.

This clause is intended to curtail the increase of political power in the individual states that might interfere with the supremacy of the federal government. Numerous controversies that arose between various colonies led to the system of allowing Congress to have a say over agreements between states. Various courts have observed that the Compact Clause requires congressional consent only if the agreement among the states tends to the increase of political power in the States, which may interfere with the supremacy of the United States.