Pursuant to paragraph (h) of Section 6 of Article VII of the Illinois Constitution of 1970 the power to regulate the licensing of plumbers, to promulgate a minimum plumbing code of standards, and to regulate the registration of irrigation contractors and plumbing contractors shall, except as may otherwise be provided within and pursuant to the provisions of Section 16 and Section 16.1 of this Act, be exercised by the State and may not be exercised by any unit of local government, including home rule units.