Massachusetts General Laws Part I. Administration of the Government (Ch. 1-182) Ch. 54, § 72

The select board, board of selectmen, town council or city council of each city and town, in consultation with its election officers and registrars, shall detail a sufficient number of police officers or constables for each building that contains the polling place for 1 or more precincts at every election therein to preserve order and to protect the election officers and supervisors from any interference with their duties and to aid in enforcing the laws relating to elections.