Mass. Gen. Laws ch. 176O § 4
A carrier, including a dental or vision carrier, shall not refuse to contract with or compensate for covered services an otherwise eligible health, dental or vision care provider solely because such provider has in good faith communicated with or advocated on behalf of one or more of his prospective, current or former patients regarding the provisions, terms or requirements of the carrier's health, dental or vision benefit plans as they relate to the needs of such provider's patients, or communicated with 1 or more of his prospective, current or former patients with respect to the method by which such provider is compensated by the carrier for services provided to the patient. Nothing in this section shall preclude a carrier, including a dental or vision carrier, from requiring a health, dental or vision care provider to hold confidential specific compensation terms.
Mass. Gen. Laws ch. 176O, § 4