Mass. Gen. Laws ch. 78, § 33

The board of trustees of a free public library in any city or town, or in the absence of such board, the city or town official possessing the appointive powers of such board, shall establish a written policy for the selection of library materials and the use of materials and facilities in accordance with standards adopted by the American Library Association. No employee shall be dismissed for the selection of library materials when the selection is made in good faith and in accordance with the approved policy adopted pursuant to the provisions of this section.