Mass. Gen. Laws ch. 136, § 6
Section five shall not prohibit the following:
(50) The keeping open of a store or shop and the sale at retail of goods therein, but not including the retail sale of goods subject to chapter 138, and the performance of labor, business, and work directly connected therewith on Sunday. This exemption shall not apply to any legal holiday as defined in clause eighteenth of section 7 of chapter 4, but this exemption shall apply to the day following Christmas Day when Christmas occurs on a Sunday. In any year in which Christmas Day occurs on a Sunday, this exemption shall not apply to that Sunday.
No employee engaged in work subject to the provisions of this clause shall be required to perform such work, and refusal to work for any retail establishment on Sunday shall not be grounds for discrimination, dismissal, discharge, reduction in hours, or any other penalty. The provisions of this paragraph shall be enforced by the office of the attorney general. The provisions of section one hundred and eighty A of chapter one hundred and forty-nine shall apply to any violation of this paragraph.