Massachusetts General Laws Part I. Administration of the Government (Ch. 1-182) Ch. 146, § 84

No person shall engage in the business of a master pipefitter, work as a journeyman or apprentice pipefitter, work as a refrigeration technician or work on a fire protection sprinkler system as a fire protection sprinkler system contractor or as a sprinkler fitter or apprentice sprinkler fitter, unless that person is lawfully licensed under section 85 or section 85A.