Mass. Gen. Laws ch. 44, § 66

In any city having a plan E or plan D charter with the approval of the city manager, in any other city with the approval of the mayor, and in towns with the approval of the selectmen, advances may be made to any officer or employee thereof in anticipation of necessary expenses authorized to be incurred under the provisions of clause (34) of section five of chapter forty subject, however, to such regulations as the treasurer thereof shall from time to time prescribe.