Mass. Gen. Laws ch. 31 § 46
A permanent employee who becomes separated from his position may, with the approval of the administrator, be reinstated in the same or in another departmental unit in a position having the same title or a lower title in the same series, provided that the appointing authority submits to the administrator a written request for such approval which shall contain the reasons why such reinstatement would be in the public interest. No such request shall be approved if the person whose reinstatement is sought has been separated from such position for over five years and there is a suitable eligible list containing the names of two or more persons available for appointment or promotion to such position; provided, however, that no such limitation shall apply to the reinstatement of persons whose qualifications for reinstatement to a former position have been determined pursuant to section eight of chapter thirty-two. If the administrator fails to approve the reinstatement of such person within thirty days after such request, the appointing authority or such person may make a written request for a hearing before the administrator, who shall hold such hearing forthwith and render his decision. Nothing herein shall affect the rights of persons to reinstatement under section thirty-nine.
The administrator shall reinstate any employee of a city or town who has been separated from a civil service position through retirement pursuant to the provisions of any law if such retirement is invalidated and the retirement allowance discontinued because the proceedings relative to such retirement were illegal or defective; and such employee applies to the administrator for reinstatement within one year after the last payment of such retirement allowance. The administrator shall reinstate such person, without loss of compensation, in the same position or in a position with the same title as that formerly held by him.
Mass. Gen. Laws ch. 31, § 46