Me. Rev. Stat. tit. 29-A, § 157

Notwithstanding this Title, the Secretary of State, in concurrence with the Commissioner of Transportation, may enter into reciprocal agreements or plans with another jurisdiction providing for the registration of vehicles on an apportionment or allocation basis. In the exercise of this authority, the Secretary of State may enter into and become a member of the International Registration Plan. Registration of vehicles under the plan must be in accordance with chapter 5, subchapter I, article 5.