Me. Rev. Stat. tit. 25, § 1708

This compact takes effect upon being entered into by 2 or more states as between those states and the Federal Government. When additional states subsequently enter into this compact, it becomes effective among those states and the Federal Government and each party state that has previously ratified the compact. When ratified, this compact has the full force and effect of law within the ratifying jurisdictions. The form of ratification must be in accordance with the laws of the ratifying state.