Me. Rev. Stat. tit. 26, § 979-K

An agreement between a bargaining agent and the public employer may provide for binding arbitration as the final step of a grievance procedure, provided that any such grievance procedure shall be exclusive and shall supersede any otherwise applicable grievance procedure provided by law. If no such provision is contained in the collective bargaining agreement, the parties shall submit their differences for resolution by the State Civil Service Appeals Board.