Mass. Gen. Laws ch. 149 § 133
In every industrial establishment and railroad establishment there shall be provided suitable, adequate and convenient water closets and washing facilities, separate for each sex and plainly so designated, of such number, in such location, and so constructed, lighted, ventilated, arranged and maintained as may be determined by such reasonable rules and regulations as the department may adopt. No person shall be allowed to use a closet or privy provided for the use of persons of the opposite sex. If any such establishment is so located that a connection with a sewer system is, in the opinion of the department, impossible or impracticable, it shall provide such suitable toilet and washing facilities as the department may require. For the purposes of this section the term "industrial establishment" shall be deemed to include public garages and premises used by express, trucking and transportation companies where persons are employed. For the purposes of this section the term "railroad establishment" shall be deemed to mean that part, division or branch of any railroad in which three or more persons are employed except where toilet and washing facilities are maintained for public use.
Mass. Gen. Laws ch. 149, § 133