A collective bargaining agreement between a public employer and a bargaining agent may provide for binding arbitration as the final step of a grievance procedure but the only grievances which may be taken to such binding arbitration shall be disputes between the parties as to the meaning or application of the specific terms of the collective bargaining agreement. An arbitrator with the power to make binding decisions pursuant to any such provision shall have no authority to add to, subtract from or modify the collective bargaining agreement.   [PL 1969, c. 424, §1 (NEW).]