Seattle’s $15 minimum-wage law has received plenty of attention from those on both sides of the issue. What has received less attention is the way in which this ordinance distinguishes between businesses—and discriminates against interstate commerce.

The ordinance separates employers into two categories, those with 500 or more employees (Schedule One) and those with fewer (Schedule Two), and mandates that the first category implement wage increases more quickly than the second. But the law creates a special rule for Seattle franchises, placing them into the first category if the total number of employees in the franchise network is 500 or more.

A group of franchise owners, led by the International Franchise Association, challenged the ordinance, to no success in the lower courts. Cato is now supporting their petition to the Supreme Court. Seattle insists that this categorization is neutral as between in-state and interstate commerce, because a franchise network could be entirely within Washington. The reality is that all Seattle franchises that are in Schedule One have either an out-of-state franchisor or are associated with out-of-state franchises of the same brand. The law thus discriminates against interstate commerce in precisely the way the Commerce Clause was intended to prevent.

When the delegates met in Philadelphia in 1787 to revise the Articles of Confederation, one of their main concerns was the protectionism the states exhibited under the Articles. As James Madison said at the time, “Most of our political evils may be traced to our commercial ones.” The Constitutional Convention debated many things between May and September 1787, but there seems to have been general agreement that the new Constitution would give Congress power to regulate—“make regular”—interstate commerce.

Although today’s federal government has far exceeded the positive Commerce Clause power the Framers intended to give it—in terms of federal programs and regulations—the principle that states and local governments may not enact laws that discriminate against interstate commerce dates back to Chief Justice Marshall’s opinion in Gibbons v. Ogden (1824), and indeed all the way to the animating purpose of the Convention. That principle—known as the negative or Dormant Commerce Clause—applies both when Congress has passed legislation in the area and when it hasn’t. See Case of the State Freight Tax (1873).

One scholar has remarked that, under the Articles, the states were “marvelously ingenious” at designing protectionist measures. Seattle’s franchise categorization is just one such measure, which discriminates against interstate commerce in a subtler way than most of the protectionism that courts have considered.

While arguing that its law is constitutional, Seattle points to the fact that the burden of the law will fall on in-state actors (the Seattle franchises). Where the burden falls, however, is irrelevant to whether a law discriminates against interstate commerce. Just last term, in Comptroller of the Treasury of Maryland v. Wynne, the Supreme Court held that Maryland’s income tax scheme violated the Commerce Clause by taxing residents on income they earned out-of-state—even though, by definition, the burden of the income tax law fell on Maryland residents. Seattle’s franchise categorization also violates the Dormant Commerce Clause’s extraterritoriality principle because it makes the wage burden placed on Seattle franchisees dependent on the hiring decisions of independent (and most likely unknown) franchises in other states.

The Supreme Court should take up International Franchise Association v. City of Seattle and consider not the economic wisdom of minimum-wage requirements generally but the effect of this particular law on interstate commerce.