State governments have broad regulatory authority. Unlike Congress, which must point to an enumerated constitutional power, states possess general police power. That means states may ordinarily regulate for the health, safety, welfare, and morals of their people. A state may regulate criminal law, property, contracts, family law, education, local business, zoning, professional licensing, and public safety without first identifying a specific constitutional grant of power.
But state power is not unlimited. The Constitution creates a national union, makes valid federal law supreme, protects interstate commerce from undue local interference, limits discrimination against citizens of other states, and prevents states from burdening the federal government itself. A state law may therefore be invalid even when the state is acting within its traditional police power.
This chapter focuses on the constitutional limits on state power. The major doctrines are preemption, the Dormant Commerce Clause, the Privileges and Immunities Clause of Article IV, state taxation of interstate activity, and intergovernmental immunity. These doctrines often appear together because they all ask whether a state has gone too far in regulating matters connected to national unity, interstate movement, or federal authority.
I Doctrinal Framework
A state-power problem usually begins from the opposite direction of a congressional-power problem. When Congress acts, ask: What enumerated power supports the federal law? When a state acts, ask: What constitutional limit restricts the state’s otherwise broad police power?
The Most Common Limits Are:
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Preemption: Valid federal law may displace state law under the Supremacy Clause.
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Dormant Commerce Clause: Even when Congress has not acted, states generally may not discriminate against or unduly burden interstate commerce.
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Article IV Privileges and Immunities: States may not discriminate against citizens of other states with respect to fundamental rights or important economic activities unless they have a substantial reason and use closely related means.
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State taxation limits: States may tax interstate activity only when the tax has a sufficient connection to the state and is fairly structured.
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Intergovernmental immunity: States may not regulate or tax the federal government in a way that interferes with federal operations or discriminates against the federal government.
The exam method is straightforward. Identify the state law, determine whether federal law exists, ask whether the state law discriminates against interstate commerce or out-of-state citizens, and then apply the relevant test.
II. State Police Power
States have broad police power. This is the power to regulate for public health, safety, welfare, and morals. It includes much of ordinary lawmaking: criminal law, tort law, property regulation, land use, professional licensing, public schools, family law, local business rules, and safety codes.
Because states possess general police power, a challenger usually cannot defeat a state law merely by arguing that the Constitution does not expressly authorize the state to act. States do not need the same kind of enumerated power that Congress needs.
But police power is subject to constitutional limits. A state may regulate restaurants for public health, but it may not enforce rules that violate equal protection. A state may license professionals, but it may not discriminate against out-of-state citizens without sufficient justification. A state may regulate local sales, but it may not protect local businesses by excluding interstate competition.
The state-power analysis therefore begins with broad state authority but quickly turns to constitutional restraints.
III Preemption and the Supremacy Clause
The Supremacy Clause provides that the Constitution and valid federal laws are supreme over conflicting state law. When valid federal law conflicts with state law, federal law controls. This is called preemption.
Preemption is not a source of federal power by itself. Congress must first act within its constitutional authority. If Congress lacked power to enact the federal statute, the statute cannot preempt state law. But when Congress validly legislates, state law must yield.
Three Major Forms of Preemption
1. Express Preemption
Occurs when Congress explicitly states that federal law displaces state law.
The main issue is statutory interpretation: What exactly did Congress preempt? A state law is not preempted simply because the federal statute contains the word “preemption.”
2. Field Preemption
Occurs when federal regulation is so pervasive that it occupies the field, leaving no room for state regulation.
More likely in areas where national uniformity is vital (e.g., immigration). Traditional state police-power areas require clearer evidence of congressional intent.
3. Conflict Preemption
Occurs when state law conflicts with federal law. Two forms:
- Impossibility: Impossible to comply with both.
- Obstacle: State law frustrates the federal scheme/purpose.
Exam Tip
In a preemption question, always ask two questions in order. First, is the federal law valid? Second, what kind of preemption is being claimed: express, field, or conflict? Do not jump straight to “federal law wins” without identifying the type of conflict.
IV Dormant Commerce Clause
The Commerce Clause gives Congress power to regulate interstate commerce. The Dormant Commerce Clause is the negative implication of that grant: even when Congress has not acted, states may not enact laws that discriminate against or unduly burden interstate commerce.
The doctrine protects national economic union. Without it, states could use local laws to favor in-state businesses, exclude out-of-state competitors, and create trade barriers among the states. The Constitution was designed in part to prevent economic Balkanization.
DCC Analysis Framework
Dormant Commerce Clause analysis usually asks whether the state law is discriminatory or evenhanded.
Discriminatory Law
Treats in-state and out-of-state economic interests differently for protectionist reasons. Discrimination may appear on the face, in its purpose, or in its practical effect.
Evenhanded Law
Applies equally to in-state and out-of-state interests but incidentally burdens interstate commerce (e.g., state safety regulations, local inspections).
Common Trap
Do not assume that every burden on interstate commerce is unconstitutional. State laws often affect interstate businesses. The Dormant Commerce Clause is most suspicious of discrimination and protectionism. Evenhanded regulations are often upheld unless the burden is clearly excessive.
V. Market Participant Exception
The market participant doctrine is an important exception. When a state acts as a market participant rather than a market regulator, it may favor its own citizens or businesses in ways that would otherwise raise Dormant Commerce Clause concerns.
For example, if a state owns a cement plant, it may choose to sell cement first to in-state buyers. If a city hires contractors for a public project, it may sometimes prefer local workers. In those situations, the government is participating in the market, much like a private buyer or seller.
But the exception has limits. A state may not use its market participation to control downstream private conduct in other markets. The more the state acts like a regulator rather than a buyer or seller, the less protection the exception provides.
VI. Congressional Authorization
Congress may authorize states to take actions that would otherwise violate the Dormant Commerce Clause. Because the Dormant Commerce Clause is inferred from Congress’s commerce power, Congress may permit state regulation of interstate commerce if it does so clearly.
This is a powerful point on exams. If Congress has unmistakably authorized state discrimination or burdens, the Dormant Commerce Clause objection may fail. The issue then becomes whether Congress had constitutional authority and whether some other constitutional limit applies.
Apple Packaging Hypothetical
"A state enacts a law prohibiting the sale of out-of-state apples unless they are packaged in the state using local facilities. The state says the law protects consumers by ensuring freshness."
The law is likely discriminatory. It burdens out-of-state apple producers and benefits local packaging facilities. Although consumer protection is a legitimate goal, the state must show that no reasonable nondiscriminatory alternative can serve that goal. The state could require freshness labels, inspection standards, or uniform packaging rules that apply to all apples regardless of origin. Because less discriminatory alternatives exist, the law is likely invalid.
Now change the facts. The state requires all apples sold in the state, whether in-state or out-of-state, to display a uniform freshness label. The law increases costs for interstate sellers but applies evenhandedly and serves a legitimate consumer-protection purpose. That law is more likely valid unless the burden on interstate commerce is clearly excessive.
VII Article IV Privileges and Immunities
The Privileges and Immunities Clause of Article IV limits discrimination by states against citizens of other states. It provides that citizens of each state are entitled to the privileges and immunities of citizens in the several states.
This clause protects national unity by preventing states from treating outsiders as political or economic enemies. It applies to discrimination against natural persons who are citizens of other states. Corporations and aliens generally do not invoke Article IV privileges and immunities.
The clause applies to fundamental rights and important economic activities, especially the pursuit of a common calling. A state may not exclude out-of-state citizens from practicing a profession, obtaining employment, owning property, accessing courts, or engaging in basic civil activities without sufficient justification.
The test asks whether the state has a substantial reason for the discrimination and whether the discriminatory means bear a close relationship to that reason.
DCC vs. Privileges & Immunities
The Dormant Commerce Clause and Article IV P&I Clause often overlap, but they are not the same.
| Feature | Dormant Commerce Clause | Article IV P&I |
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| Who it protects | Individuals and Corporations. | Only Natural Persons (citizens of other states). |
| Focus | Discrimination against or burdens on interstate economic activity. | Discrimination regarding fundamental rights and important economic activities (e.g., earning a living). |
| Market Participant Exception | Yes, it applies. | No, it does not apply. |
| Congressional Authorization | Congress can authorize DCC violations. | Congress cannot authorize Art IV P&I violations. |
Exam Tip: When a state discriminates against outsiders, ask two separate questions. Is the state discriminating against interstate commerce? That suggests DCC. Is the state discriminating against citizens of other states in pursuing important livelihoods? That suggests Art IV P&I.
VIII State Taxation of Interstate Commerce
States may tax interstate commerce, but constitutional limits prevent unfair or protectionist taxation. A state tax affecting interstate commerce is generally valid if it satisfies four requirements.
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Substantial Nexus: The taxpayer or transaction must have a meaningful connection to the taxing state.
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Fair Apportionment: The state may tax only its fair share of interstate activity and may not create a serious risk of multiple taxation.
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Nondiscrimination: A state may not structure taxes to favor local businesses over out-of-state competitors.
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Fair Relation to Services: The taxpayer’s connection to the state should justify requiring contribution to state services and infrastructure.
User Fees and State Charges
States may charge fees for use of state facilities, such as roads, ports, airports, or inspection services. A user fee is more likely valid when it is based on a fair approximation of use, is not excessive in relation to the benefits provided, and does not discriminate against interstate commerce.
For example, a state may charge trucks a reasonable fee for use of state highways. But a fee designed to shift costs onto out-of-state truckers while sparing local businesses may be unconstitutional. The label is not controlling. Calling a charge a “fee” does not save it if it operates as a discriminatory tax or trade barrier.
IX. Intergovernmental Immunity
Intergovernmental immunity protects the federal government from improper state interference. States may not regulate the federal government directly or discriminate against the federal government or those with whom it deals.
The principle follows from federal supremacy. If states could tax or regulate federal operations at will, they could obstruct national policy. A state may not require a federal agency to obtain a state license before performing federal functions. Nor may it impose a special tax that singles out federal contractors for unfavorable treatment.
However, generally applicable state laws may sometimes affect federal contractors or federal employees in ordinary ways. The key question is whether the state is regulating the federal government directly, discriminating against it, or substantially interfering with federal operations.
Common Trap: Do not confuse intergovernmental immunity with ordinary preemption. Preemption asks whether federal law displaces state law. Intergovernmental immunity asks whether the state is improperly regulating, taxing, or discriminating against the federal government itself, even apart from a specific preemption clause.
The 21st Amendment and State Alcohol Regulation
State alcohol regulation sometimes appears in Dormant Commerce Clause problems. The Twenty-First Amendment gives states substantial authority over alcohol importation and distribution. But that authority does not automatically permit economic protectionism.
A state may regulate alcohol for legitimate purposes such as temperance, orderly markets, and public safety. But a state law favoring in-state alcohol producers or retailers over out-of-state competitors may still be vulnerable if its real function is protectionist. The exam point is modest: alcohol is special, but not a constitutional free zone. State authority is broader, yet still constrained by principles of nondiscrimination.
X Application and Analysis
The Food Truck Hypothetical
"A state imposes a special $500 annual license fee on out-of-state food trucks that operate at local festivals. In-state food trucks pay $50. The state says the higher fee compensates for enforcement costs."
Dormant Commerce Clause Analysis:
This law discriminates against interstate commerce on its face. The state must show a legitimate local purpose that cannot be served by reasonable nondiscriminatory alternatives. A uniform fee based on actual inspection costs would likely be a less discriminatory alternative.
Privileges and Immunities Analysis:
It also burdens out-of-state citizens who pursue a common calling (if the operators are natural persons). Under Article IV, the state must show a substantial reason for treating nonresidents differently and a close relationship between the discrimination and that reason. Mere revenue protection or favoritism for local vendors is not enough. The law is likely invalid.
The Milk Processing Analysis
"Consider a state law requiring all milk sold in the state to be processed at an in-state facility. The state argues that in-state processing makes inspections easier and protects public health."
Begin with the Dormant Commerce Clause. The law discriminates against interstate commerce. Public health is a legitimate local interest, but the state must show that nondiscriminatory alternatives are inadequate (e.g., testing at point of sale, certification).
Now consider preemption. If federal law creates a comprehensive national milk-safety system and expressly prohibits states from imposing additional processing-location requirements, the state law is expressly preempted. If not express, field or obstacle preemption may apply.
Finally, consider whether Congress authorized the state rule. If Congress clearly permitted states to impose in-state processing requirements, the DCC challenge would be weaker because Congress may authorize state burdens on interstate commerce. But other constitutional objections could still remain.
XI. Bar-Style Analysis Notes
A strong state-power answer should begin by identifying the state law and the affected parties. Is the state regulating goods, services, employment, licensing, taxation, access to public benefits, or federal operations?
- Next, ask whether federal law exists. If so, analyze preemption. Identify express preemption, field preemption, or conflict preemption. Be precise. Do not merely announce that federal law “occupies the area” unless the facts support that conclusion.
- Then ask whether the state law discriminates against interstate commerce. If it does, apply the demanding strict scrutiny test. If the law is evenhanded, balance the local benefits against the burden on interstate commerce (Pike balancing).
- Then consider Article IV Privileges and Immunities if the law discriminates against out-of-state citizens with respect to important rights or economic activities (remember: natural persons, not corporations).
- If the law is a tax or fee, apply the state-taxation requirements: substantial nexus, fair apportionment, nondiscrimination, and fair relation to state services.
- If the state law affects the federal government, consider intergovernmental immunity. Ask whether the state is directly regulating, discriminating against, or substantially interfering with federal functions.
- Finally, conclude with the likely result. Explain whether the state law is valid, preempted, discriminatory, excessively burdensome, or unconstitutional.
Common Trap: Do not collapse all federalism doctrines into one general fairness test. Preemption, Dormant Commerce, Privileges and Immunities, state taxation, and intergovernmental immunity each ask different questions. The best exam answers separate them cleanly.
Chapter Summary
States have broad police power to regulate health, safety, welfare, and morals. But state power is limited by the Constitution’s commitment to federal supremacy, national economic union, equal treatment of out-of-state citizens, fair taxation of interstate activity, and protection of federal operations.
Preemption occurs when valid federal law displaces state law. Express preemption depends on statutory text. Field preemption applies when federal regulation occupies an area. Conflict preemption applies when compliance with both state and federal law is impossible or when state law obstructs federal purposes.
The Dormant Commerce Clause limits state discrimination against or undue burdens on interstate commerce, even when Congress has not acted. Discriminatory laws are usually invalid unless the state shows a legitimate local purpose that cannot be served by reasonable nondiscriminatory alternatives. Evenhanded laws are generally upheld unless their burdens on interstate commerce are clearly excessive in relation to local benefits. The market participant exception allows states more freedom when acting as buyers or sellers rather than regulators. Congress may also authorize state burdens on interstate commerce.
Article IV Privileges and Immunities prevents states from discriminating against citizens of other states with respect to fundamental rights and important economic activities. The state must have a substantial reason for the discrimination, and the means must closely relate to that reason.
State taxation of interstate commerce is valid only when the tax has a substantial nexus to the state, is fairly apportioned, does not discriminate against interstate commerce, and is fairly related to services provided by the state. User fees must be reasonable and nondiscriminatory.
Intergovernmental immunity prevents states from directly regulating, taxing, or discriminating against the federal government in ways that interfere with federal operations.
The central lesson is that state police power is broad but not supreme. A state may regulate local matters, protect public health, and structure its economy, but it may not conflict with valid federal law, build economic barriers against other states, discriminate against outsiders without sufficient justification, impose unfair taxes on interstate activity, or control the federal government.
Practice Quiz
Test your knowledge of State Power, Preemption, and the Dormant Commerce Clause.
Knowledge Check
Master Chapter 4's vocabulary. Click any card to flip it.