This is a voluntary fee. No one has to pay it. You only have to pay it if you choose not to use reusable bags.
— Seattle city council president Richard Conlin, who worked with Mayor Greg Nickels on the proposal to levy a 20 cent tax on shoppers at grocery, drug, and convenience stores for each paper or plastic bag they use.
Hat tip: Jacob Sullum, who points out that by the same reasoning, income tax, sales tax, tobacco tax and property tax are all ‘voluntary’.