The Interstate Environmental Commission, with which NEIWPCC works, is an interstate compact. Others include the Driver License Compact (coordination of driver-license information), the Atlantic States Marine Fisheries Commission, and the New York–New Jersey Port Authority Compact of 1921.
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.