Mass. Gen. Laws ch. 149, § 101

The preceding section shall not apply to iron works, glass works, paper mills, letterpress establishments, print works, bleaching works, or dyeing works; and the attorney general, if it is proved to his satisfaction that in any other factories or workshops or mechanical establishments it is necessary, by reason of the continuous nature of the processes or of special circumstances affecting such establishments, including collective bargaining agreements to exempt them from the preceding section and that such exemption can be made without injury to the persons affected thereby, may grant such exemption as, in his discretion, seems necessary.