Mass. Gen. Laws ch. 152 § 20A
Any employer who maintains a clinic, dispensary or hospital for the treatment of injured employees and any insurer who maintains a clinic, dispensary or hospital for the treatment of injured employees of any insured shall, upon request of any injured employee attending such a clinic, dispensary or hospital, or of his attorney, furnish such employee or his attorney, at cost, with copies of reports of all medical examinations of the injured employee made while at such clinic, dispensary or hospital, showing the history obtained, the nature of the treatment given or prescribed, the diagnosis and the prognosis. No such medical report shall upon objection by the claimant be admissible in evidence in any proceeding under this chapter, unless a copy thereof has been furnished to the claimant, or a person acting in his behalf, or to his attorney, within twenty days after a written request therefor.
Mass. Gen. Laws ch. 152, § 20A