Me. Rev. Stat. tit. 22, § 3955

The State may enter into agreements with Indian tribes with respect to the care and custody of Indian children and jurisdiction over Indian child custody proceedings, including agreements that provide for orderly transfer of jurisdiction on a case-by-case basis and agreements that provide for concurrent jurisdiction between the State and Indian tribes. A revocation of an agreement under this section does not affect any action or proceeding over which a court has already assumed jurisdiction, unless the agreement provides otherwise.