An appointing authority, with the approval of the administrator, may promote an employee in the official service from one title to the next higher title in the same series in the same departmental unit, subject to the following requirements:
In case of promotional appointments of more than one employee, the appointing authority may select from among the same number of employees with the greatest length of service as the number provided in the civil service rules governing appointments to fill more than one vacancy.
The effective date of a promotional appointment made pursuant to this section shall be the date on which the person promoted assumes the duties of the higher title, as certified by the appointing authority, following the approval of the promotion by the administrator.
The provisions of this section may be utilized to make a temporary promotional appointment to fill a temporary vacancy in a permanent position if the administrator is satisfied that such vacancy is likely to become permanent within a reasonable period of time. If a person has received such a promotional appointment, the administrator, upon the request of the appointing authority, may approve such promotional appointment on a permanent basis when the position to which the temporary promotional appointment has been made becomes permanently vacated.
Mass. Gen. Laws ch. 31, § 8