Mass. Gen. Laws ch. 142 § 21A
Notwithstanding the provisions of any general or special law to the contrary, no licensed plumber or gas fitter, acting in the capacity of a self-employed contractor, shall be issued a permit for the performance of plumbing and gas fitting, pursuant to this chapter unless the licensee has a current liability insurance policy including completed operations coverage, which has been issued by an insurance company licensed to do business within the commonwealth, or other type of indemnity against liability providing substantially equivalent coverage, or a bond. The licensee shall check the appropriate block on the uniform application to perform plumbing and gas work.
In lieu of such insurance requirement, plumbing and gas inspectors shall accept the signature of the owner or his agent on the uniform application for a permit to perform plumbing or gas work upon the property of said owner.
Mass. Gen. Laws ch. 142, § 21A