Note: Please remember that a flowchart like this is inherently limited, and that the law as developed by the courts is always more complicated by loose ends than a flowchart like this can reflect.

Question 1. Does the law at issue treat people (or entities) residing (or located) outside a particular area differently from the way it treats similarly situated people (or entities) residing (or located) inside that area? If so, it discriminates against interstate commerce "on its face" and is subject to the "strictest scrutiny," Hughes v. Oklahoma. Go to Question 7. If not, go to Question 2.

Question 2. Does the law prevent people from entering or leaving a particular area, or prevent them from bringing something into or out of a particular area? If so, it discriminates against interstate commerce "on its face" and is subject to the "strictest scrutiny," Hughes v. Oklahoma. Go to Question 7. If not, go to Question 3.

Question 3. Does the law prevent people from entering or leaving a particular area, or prevent them from bringing something into or out of a particular area, unless a condition is fulfilled? If so, the law discriminates against interstate commerce "on its face" and is subject to the "strictest scrutiny," Hughes v. Oklahoma. Go to Question 7. If not, go to Question 4.

Question 4. In light of economic reality, does the law almost invariably affect people (or entities) residing (or located) outside a particular area differently from the way it affects similarly situated people (or entities) residing (or located) inside that area? If so, the law discriminates against interstate commerce "in practical effect" and is subject to the "strictest scrutiny," Hughes v. Oklahoma. Go to Question 7. If not, go to Question 5.

Question 5. Does the law "regulate evenhandedly with only 'incidental' effects on interstate commerce"? Hughes v. Oklahoma. If so, go to Question 6. If not, the law does not implicate the Dormant Commerce Clause (assuming the answer to Questions 1-4 was also "no").

Question 6. Does the negative impact of the law on interstate commerce clearly exceed its value in terms of the police power (that is, its value in promoting the health, welfare, safety, and morals of the population)? If so, the law violates the Constitution. If not, the law is constitutional. (Note: In theory, a court could ask at this point if the government has a reasonable non-discriminatory alternative, but the Court has never based a decision on this issue when applying the Dormant Commerce Clause in this context.)

Question 7. Does the law serve a "legitimate local purpose"? Hughes v. Oklahoma. If not, it violates the Constitution. If so, go to Question 8. (Remember that economic protectionism for its own sake is not a legitimate local purpose.)

Question 8. Does the government have a reasonable non-discriminatory alternative? If so, the law violates the Constitution. If not, the law is constitutional.

Note 1. Remember the market-participant exception.

Note 2. Remember that Congress may enact laws that negatively affect interstate commerce or even discriminate against interstate commerce.

Note 3. Remember the Privileges and Immunities Clause of Article IV.

Note 4. For some justices, direct evidence that the government enacted a law with a motive of economic protectionism is sufficient to justify striking it down. See Kassel v. Consolidated Freightways Corp. (Brennan, J., joined by Marshall, J.).

Problem 1. State issues an exclusive license to D to run steamboats on its waterways. P is prosecuted for running a steamboat on these waterways. Assume no federal legislation controls.

Problem 2. State hires D to build a dam across a stream in order to flood a marsh where mosquitoes breed. P's boat hits the dam and sustains damages. P sues D for tort. D argues that State told him to build the dam. P says that State lacks to authority to block the stream. Assume the stream is part of an interstate waterway.

Problem 3. City requires boat owners to hire a local pilot when entering or leaving its port. P is prosecuted for failing to hire a local pilot while entering City's port. Assume no federal legislation controls.

Problem 4. State prohibits trucks wider than 7-½ feet or heavier than 10 tons. Most trucks in the U.S. are 8 feet wide and weigh 16 to 18 tons. State claims its highways cannot sustain heavy trucks because they lack a longitudinal joint, and that many of its highways are exceedingly narrow. P is prosecuted for driving an 18-ton truck on one of State's highways.

Problem 5. State prohibits freight trains with more than 70 cars. Because trains cannot be broken up and reassembled easily, railroad P, which runs through State, must run a large number of short trains over much of its route, including much territory outside of State. Evidence indicates that not much safety, if any, is achieved by running shorter trains. State prosecutes railroad for running a long train.

Problem 6. State requires trucks to have contoured mudguards. Another state requires square mudguards. Other states permit either kind of mudguard. Some evidence indicates that all kinds of mudguards are equally effective. Other evidence indicates that square mudguards are better than contoured mudguards. Trucking company P brings an action in equity against State's attorney general, seeking to restrain enforcement of the requirement.

Problem 7. State prohibits double-trailer trucks with a total length of more than 55 feet. Certain counties bordering states that permit longer double-trailer trucks may opt out of this prohibition, but the remaining counties may not opt out. Some evidence indicates that the border counties wanted the business associated with long two-trailer trucks. Other evidence indicates that State did not want such trucks traveling across State in interstate travel. Most double-trailer trucks in the U.S. are 65 feet in total length. Trucking company P brings an action in equity against State's attorney general to enjoin enforcement of the prohibition.

Problem 8. State prohibits the retail sale of milk within its borders unless the seller certifies that it purchased the milk at wholesale for at least $1.00 per gallon. Producers in State cannot sell milk for less than $1.00 per gallon without losing money. Producers in a nearby state can sell milk for $0.50 per gallon and still make money. Out-of-state producer P brings an action in equity against the State's Commissioner of Farms and Markets to enjoin enforcement of the prohibition.

Problem 9. State will not allow milk to be sold at retail within its borders for less than $2.00 per gallon. Retailers who purchase milk from producers in a nearby state could easily sell milk at retail within State for $1.50 per gallon and still make money. Retailer P who has habitually purchased milk from producers in this nearby state sues State's Commissioner of Farms and Markets to enjoin the floor price.

Problem 10. State will not allow milk to be purchased from producers in the state for less than $1.00 per gallon. Wholesaler P, who habitually purchases milk from producers in State but who habitually wholesales milk outside of State, sues State's Commissioner of Farms and Markets to enjoin the floor price.

Problem 11. State imposes a tax of 2% on the sale of goods within its borders. State also imposes a tax of 2% on the "use" of goods within its borders that were not purchased within State. P refuses to pay the use tax and brings an action in equity against State's tax collector to enjoin enforcement of the tax.

Problem 12. Commissioner of Farms and Markets of State issues licenses for milk pasteurization plants. P applies for a license. Commissioner refuses to issue a license because P admits that most of the milk pasteurized at the plant will be shipped to another state. Commissioner justifies her decision on the ground that the people in the area of the proposed plant need greater access to milk. P brings an action in equity against the Commissioner to require her to issue the license.

Problem 13. City prohibits the sale within its limits of milk that is not pasteurized within five miles of the center of town. Milk pasteurizer P, which is located in another state, brings an action against City to restrain enforcement of the prohibition. City argues that locally pasteurized milk is better milk because City's testers are better trained and use more exacting standards than other testers. P responds that City could send its testers to P's plant, where they could apply their own standards. City responds that this never works, because of endless litigation concerning payment for its testers' expenses.

Problem 14. State prohibits the shipment of minnows seined in its waters to other states for commercial sale. State argues that it must limit the number of minnows seined in its waters for environmental reasons.

Problem 15. State requires that apples sold within its border must bear a "USDA grade and no other" on their container. Another state with a significant apple industry has its own set of standards for grading apples. These standards are more exacting than those of State. Apple growers in this other state must relabel their containers. They also lose whatever advantage their labeling system provides. State argues that the other state's labels are confusing to consumers. Apple grower P, who is from this other state, brings an action in equity against State's Commissioner of Farms and Markets, who is charged with enforcing the requirement.

Problem 16. If a customer buys natural gas from a local utility, State imposes no tax. But if a customer purchases gas directly from an out-of-state producer and takes gas directly from the pipeline, State does impose a tax. P, who buys gas from an out-of-state producer and takes gas directly from the pipeline, sues State's tax collector in equity, seeking to restrain collection of the tax. Evidence indicates that the gas utilities industry and the interstate direct-from-the-pipeline industry are distinct and have distinct regulatory regimes, even though the commodity at issue is identical, and even though natural gas sold by utilities initially arrives in State via the pipeline.

Problem 17. State requires all growers of raisins within State to transfer two-thirds of their output to State. State then sells at will when the market is right, allocating proceeds among growers. Almost all raisins end up sold in other states.

Problem 18. City is under pressure to improve the handling of solid waste within its borders. City enters to a contract with a private company, pursuant to which the private company will build and operate a state-of-the-art transfer station. City guarantees that all solid waste that is generated or brought within its borders will be taken to the station, and that the station will be permitted to charge an above-market "tipping fee" for all waste delivered to the plant. (The monopoly and the above-market fee guarantee an adequate return on the private company's investment.) At the end of five years, City will purchase the station from the company for $1.00. Trash hauling company P is cited for attempting to deliver solid waste to a recycling plant located in another state.