Mass. Gen. Laws ch. 152, § 55A

Notwithstanding any general or special law to the contrary, a mid-term notice of cancellation of a workers' compensation policy shall be effective only if based on one or more of the following reasons: (i) nonpayment of premium; (ii) fraud or material misrepresentation affecting the policy or insured; (iii) a substantial increase in the hazard insured against. Nothing in this section shall limit an insurer's right to refuse to renew a workers' compensation policy.