Massachusetts General Laws Part I. Administration of the Government (Ch. 1-182) Ch. 41, § 133

(a) The initial appointment shall be for a period of one year during which a person shall actually perform the duties of such position on a full-time basis. The initial appointment shall be a probationary period during which police officers shall be deemed employees at will whose removal or dismissal shall be without recourse at any time during such initial appointment.

(b) Appointment subsequent to the initial appointment shall be made annually or for a term of years as the appointing authority shall determine, or for an unspecified or indefinite term of appointment as long as the officer is not removed as described in this paragraph. The appointing authority may remove any such officer for cause, or for some other standard contained in an applicable collective bargaining agreement or employment contract, and after a hearing, at any time during such appointment. For police officers covered by collective bargaining agreements or employment contracts which contain standards for the discharge, termination or removal of employees, the non-reappointment of a police officer serving under an appointment subsequent to an initial appointment shall be considered to be a discharge, termination or removal and the standards shall be enforceable with respect to such non-reappointment by the procedures set forth in the collective bargaining agreement or employment contract.