Fortunately, CMRs don't have quite the same bite as MGLs, but they are still real. . . .
Herewith, for what it may be worth, my take on the issue of carrying in a Massachusetts licensed gaming casino and 205 CMR § 138.20:
Interpretive vs. Legislative. With respect to regulations promulgated by Massachusetts executive agencies, the term “regulation” is potentially ambiguous.
Agencies may promulgate “interpretive regulations,” which are nothing more than advance notice as to how an agency interprets the terms of an act of the General Court,
i.e., what position the Agency will take on the meaning of a regulation if the question ever arises in court. Interpretive regulations have no force of law and will be reviewed de novo by a court.
“Legislative regulations” amount to an exercise of the General Court’s otherwise exclusive power to enact laws, which the General Court has limited power
[1] to delegate to an executive agency. A legislative regulation must derive from a specific such delegation contained in the Agency’s organic statute.
The Gaming Commission. While I have not done specific research on the point (and don’t intend to), my take on § 138.20 is that it is a legislative regulation promulgated under a delegation by the General Court to the Gaming Commission to enact regulations governing the conditions under which the Commission can license conduct by gaming licensees. So far as I am aware, the General Court has not delegated power to the Gaming Commission to promulgate regulations governing the conduct of the public at large, or even those attending a gaming facility. This is consistent with the actual language of § 138.20, which by its terms addresses only a purported condition of a gaming license directing action by the gaming licensee.
As a result, my take is that § 138.20 does not make carrying a firearm by a member of the public a crime. Rather, the “notice” the posting of which by a gaming licensee is mandated by § 138.20, has no greater (or lesser) legal effect than any other “No Guns on Premises” notice posted by any other owner of premises.
That said, I am not addressing the issue of whether, even if not criminal, carrying a firearm when visiting a casino is wise. Or, for that matter, whether visiting a casino (armed or not) is wise.
[1] For those interested in the “non-delegation” doctrine, see Benjamin M. McGovern,Reexamining the Massachusetts Nondelegation Doctrine: Is the "Areas ofCritical Environmental Concern" Program an Unconstitutional Delegation of Legislative Authority?", 31B.C. Envtl. Aff. L. Rev. 103 (2004),
http://lawdigitalcommons.bc.edu/ealr/vol31/iss1/5