Mentioned in the U.S. Constitution, sometimes expressly authorized by Congress, interstate compacts like NEIWPCC are voluntary agreements among states to work together on specified matters of common concern.

The Interstate Environmental Commission, which serves several NEIWPCC states, is an interstate compact. Others include

NEIWPCC was created by Congress in 1947. Over a period of years our seven member states each enacted legislation joining the compact.

The Supreme Court has ruled that Congressional authorization is only required for compacts that would “increase…power of the states” so as to “encroach upon or interfere with the just supremacy of the United States.”

Treaties made between states under the Articles of Confederation are today treated as interstate compacts.