Mass. Gen. Laws ch. 31 § 59
Original and promotional appointments in police and fire forces of cities and of such towns where such forces are within the official service, including appointments to the position of chief or similar position where the civil service law and rules are applicable to such position, shall be made only after competitive examination except as otherwise provided by section sixty and by sections thirty-six and thirty-six A of chapter forty-eight.
An examination for a promotional appointment to any title in a police or fire force shall be open only to permanent employees in the next lower title in such force, except that if the number of such employees, or the number of applicants eligible for the examination is less than four, the examination shall be opened to permanent employees in the next lower titles in succession in such force until either four such eligible employees have applied for examination or until the examination is open to all permanent employees in lower titles in such force; provided, however, that no such examination shall be open to any person who has not been employed in such force for at least one year after certification in the lower title or titles to which the examination is open; and provided, further, that no such examination for the first title above the lowest title in the police or fire force of a city or town with a population in excess of fifty thousand shall be open to any person who has not been employed in such force in such lowest title for at least three years after certification.
Persons referred to in this section as being permanent employees in the lowest or lower title shall include only full-time members of the regular force and shall not include members of the reserve or intermittent police or fire force or members of the call fire force unless the appointing authority certifies to the administrator that the number of permanent full-time members of the regular force is insufficient to allow adequate competition in an examination and the administrator determines that the circumstances warrant opening the examination to permanent members of the reserve, intermittent or call force, as the case may be. Upon the request of the appointing authority, the administrator may include service actually performed while a permanent member of a reserve, intermittent, or call force in computing length of service required for admission to an examination for promotional appointment to the first title above the lowest title. The appointing authority shall submit with such request payroll records proving that such service was actually performed. For purposes of this section, two hundred and fifty days, or the equivalent thereof, of such service shall be equivalent to one year of service on a full-time basis in such regular force.
All promotional appointments to fill positions in regular police or fire forces shall be made on a full-time basis. No such promotional appointments shall be made on a permanent intermittent basis. No examination shall be required for promotional appointments of call men within any call fire force to which the civil service law and rules are applicable.
An eligible list established as a result of any examination shall not be used for an original or promotional appointment to any position in a police or fire force unless the announcement of such examination identified such position as one to be filled from such list. Notwithstanding the provisions of any law or rule to the contrary, a member of a regular police force or fire force who has served as such for twenty-five years and who passes an examination for promotional appointment in such force shall have preference in promotion equal to that provided to veterans under the civil service rules.
Mass. Gen. Laws ch. 31, § 59