No tax is imposed by this article with respect to any transaction in interstate commerce
or otherwise to the extent to which such business may not, under the constitution
and statutes of the United States, be made the subject of taxation by this state or
any political subdivision thereof; nor shall any persons engaged in the business of
distributing, supplying, furnishing or selling gas or electricity, or engaged in the
business of transmitting messages, be subject to taxation under the provisions of
this article for such transactions as are or may become subject to taxation under
the provisions of the Municipal Retailers' Occupational Tax Act authorized by section
8-11-1 of the Illinois Municipal Code (65 ILCS 5/8-11-1).