Merchant charging the customer for a bag is voluntary

According to the Ordinance 2018-63 it is voluntary that the merchant can charge the customer to put the item in a paper bag.  The fines are only if a plastic bag appears at the check out line.  Here is the link proving the charge is voluntary http://www.muni.org/Departments/SWS/Customer_Service/Documents/plastic%20bag%20ordinance.pdf