Congress has the power to legislate under the commerce clause and often does legislate. For example, Congress might say that trucks moving on interstate highways must not be more than seventy feet in length. But if Congress does not exercise its powers and regulate in certain areas (such as the size and length of trucks on interstate highways), states may make their own rules. States may do so under the so-called historic police powers of states that were never yielded up to the federal government.

These police powers can be broadly exercised by states for purposes of health, education, welfare, safety, morals, and the environment. Police powers are the fundamental ability of a government to enact laws to coerce its citizenry for the public good, although the term eludes an exact definition. The term does not directly relate to the common connotation of police as officers charged with maintaining public order, but rather to broad governmental regulatory power. For example: fire and building codes, antidiscrimination laws, parking regulations, zoning restrictions, licensing requirements, and thousands of other state statues covering almost every aspect of life have been enacted pursuant to a state’s police powers.

The division of police power in the United States is delineated in the Tenth Amendment, which states that “[t]he powers not delegated to the United States by the Constitution, nor prohibited by it to the states, are reserved to the states respectively, or to the people.” That is, in the United States, the federal government does not hold a general police power but may only act where the Constitution enumerates a power. It is the states, then, who hold the general police power.

But the Supreme Court has reserved for itself the power to determine when state action is excessive, even when Congress has not used the commerce clause to regulate. This power is claimed to exist in the dormant commerce clause.

The commerce clause gives the national government the exclusive authority to regulate commercial activities that substantially affects trade and commerce among the states. This express grant of authority to the national government, which is often referred to as the “positive” aspect of the commerce clause, implies a negative aspect of the clause – that the states do not have the authority to regulate interstate commerce. This negative aspect of the commerce of the commerce clause is often referred to as the “dormant” (implied) commerce clause. The dormant clause comes into play when state regulations affect interstate commerce. In this situation, the courts normally weigh the state’s interest in regulating a certain matter against the burden that the state’s regulation places on interstate commerce.

There are two ways that a state may violate the dormant commerce clause. If a state passes a law that is an “undue burden” on interstate commerce or that “discriminates” against interstate commerce, it will be struck down. Kassel v. Consolidated Freightways, in Section 4.7 “Summary and Exercises”, is an example of a case where Iowa imposed an undue burden on interstate commerce by prohibiting double trailers on its highways.Kassell v. Consolidated Freightways, 450 US 662 (1981). Iowa’s prohibition was judicially declared void when the Supreme Court judged it to be an undue burden.

Discrimination cases such as Hunt v. Washington Apple Advertising Commission (Section 4.6 “Cases”) pose a different standard. The court has been fairly inflexible here: if one state discriminates in its treatment of any article of commerce based on its state of origin, the court will strike down the law. For example, in Oregon Waste Systems v. Department of Environmental Quality, the state wanted to place a slightly higher charge on waste coming from out of state.Oregon Waste Systems v. Department of Environmental Quality, 511 US 93 (1994). The state’s reasoning was that in-state residents had already contributed to roads and other infrastructure and that tipping fees at waste facilities should reflect the prior contributions of in-state companies and residents. Out-of-state waste handlers who wanted to use Oregon landfills objected and won their dormant commerce clause claim that Oregon’s law discriminated “on its face” against interstate commerce. Under the Supreme Court’s rulings, anything that moves in channels of interstate commerce is “commerce,” even if someone is paying to get rid of something instead of buying something.

Thus the states are bound by Supreme Court decisions under the dormant commerce clause to do nothing that differentiates between articles of commerce that originate from within the state from those that originate elsewhere. If Michigan were to let counties decide for themselves whether to take garbage from outside of the county or not, this could also be a discrimination based on a place of origin outside the state. (Suppose, for instance, each county were to decide not to take waste from outside the county; then all Michigan counties would effectively be excluding waste from outside of Michigan, which is discriminatory.)Fort Gratiot Sanitary Landfill v. Michigan Dep’t of Natural Resources, 504 US 353 (1992).

The Supreme Court probably would uphold any solid waste requirements that did not differentiate on the basis of origin. If, for example, all waste had to be inspected for specific hazards, then the law would apply equally to in-state and out-of-state garbage. Because this is the dormant commerce clause, Congress could still act (i.e., it could use its broad commerce clause powers) to say that states are free to keep out-of-state waste from coming into their own borders. But Congress has declined to do so. What follows is a statement from one of the US senators from Michigan, Carl Levin, in 2003, regarding the significant amounts of waste that were coming into Michigan from Toronto, Canada.