Mass. Gen. Laws ch. 71 § 43
The salary of no teacher employed with professional teacher status in any city or town except Boston shall be reduced without his consent except by a general salary revision affecting equally all teachers of the same salary grade in the town or except in connection with a reduction in status from full-time to part-time pursuant to a reduction in force resulting from declining enrollments or other budgetary reasons or pursuant to reorganizations for academic or budgetary reasons. Nothing in this section or in any other section of this chapter shall be construed to prevent a school district from entering into an individual annuity contract for such employee or from reducing the salary or compensation of such employee pursuant to such agreement for the purpose of such purchase as authorized by section thirty-seven B.
Mass. Gen. Laws ch. 71, § 43