Mass. Gen. Laws ch. 112, § 12X

Any contract or agreement which creates or establishes the terms of a partnership, employment, or any other form of professional relationship with a physician registered to practice medicine pursuant to section two, which includes any restriction of the right of such physician to practice medicine in any geographic area for any period of time after the termination of such partnership, employment or professional relationship shall be void and unenforceable with respect to said restriction; provided, however, that nothing herein shall render void or unenforceable the remaining provisions of any such contract or agreement.