Mass. Gen. Laws ch. 147 § 17B
Notwithstanding the provisions of any general or special law to the contrary, the services of all regular or permanent police officers of every city and town which accepts this section shall be restricted to five days and to forty hours in any one week; provided, that service in excess of the aforesaid days and hours may be authorized by the police commissioner, chief, superintendent or other officer or board at the head of the police department of any such city or town and the officer performing such additional service shall be compensated at the hourly rate of his regular compensation for his average weekly hours of regular duty or such higher rate as may be determined by the person or persons authorized to establish pay scales in the respective police departments. The compensation payable to any such police officer shall not be reduced by reason of the acceptance of this section. This section shall take effect in a city having a Plan E or Plan D charter when accepted by the affirmative vote of a majority of the city council and in the case of other cities by vote of the city council, subject to the provisions of its charter, and in a town by a majority vote at the annual town meeting.
Mass. Gen. Laws ch. 147, § 17B