Mass. Gen. Laws ch. 176I § 4
An organization shall not refuse to enter into a preferred provider arrangement with a health care provider on the basis of religion, race, color, national origin, age, sex, marital status, sexual orientation, or such provider's relationships with any other organization. The selection of preferred providers shall be based primarily on cost, availability and quality of covered services. The terms and conditions offered by an organization that must be met or agreed to by physicians and other professional providers of health care services desiring to enter into a preferred provider arrangement shall be subject to the disapproval of the commissioner if said terms and conditions are not consistent with the purposes, policies and provisions of this chapter.
Mass. Gen. Laws ch. 176I, § 4