States do have to follow federal laws, but only federal laws Congress had the constitutional authority to pass, and only to the extent those laws actually conflict with what a state is doing. Whether states have to follow federal laws in any given situation depends on three things: whether Congress was acting within its enumerated powers, whether the federal law was meant to displace state law or set a minimum standard, and whether the federal government is trying to force state officials to do the enforcing. Get those three answers, and you know where a state stands.
The Supremacy Clause and Its Built-In Limit
Article VI, Clause 2 of the Constitution — the Supremacy Clause — declares that the Constitution, federal statutes, and U.S. treaties are “the supreme Law of the Land,” and that state judges are bound by them even when their own state’s constitution or laws say otherwise.1Library of Congress. Article VI Clause 2 – Supreme Law Chief Justice John Marshall put teeth in that clause in McCulloch v. Maryland (1819), holding that states “have no power, by taxation or otherwise, to retard, impede, burthen, or in any manner control” the constitutional operations of the federal government.2Justia U.S. Supreme Court Center. McCulloch v Maryland, 17 US 316 (1819)
Read the clause carefully, though. Federal law is supreme only when it is “made in Pursuance” of the Constitution. If Congress passes a statute that goes beyond its enumerated powers, that statute is not supreme. It is unconstitutional, and courts can strike it down. Supremacy is real, but it is not unlimited.
What States Keep for Themselves
The Tenth Amendment sets the other side of the line: “The 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.”3Cornell Law School Legal Information Institute. Tenth Amendment, US Constitution The federal government can act only where the Constitution has given it authority. Everything else is state territory.
That territory is large. Marriage, divorce, custody, and adoption; most criminal law; professional licensing; land use and zoning; public education; and the general regulation of health, safety, and welfare all sit primarily with the states. These are the police powers, and they cover most of the law that touches daily life. Your doctor, your lawyer, your barber, and your real estate agent are all licensed by state boards, not by Washington. In those areas, the Supremacy Clause has nothing to override, because Congress has no authority to be there in the first place.
When Federal Law Is a Floor Instead of a Ceiling
A common assumption is that federal law caps what states can require. Often it does the opposite. Congress frequently sets a minimum standard and leaves states free to be stricter.
The federal minimum wage is $7.25 per hour, and has been since 2009. Most states have set their own minimums higher. Washington state, for instance, requires over $16 per hour. Those higher state wages are lawful because the federal figure is a floor: employers must pay at least $7.25, and nothing stops a state from demanding more. The same pattern shows up in environmental rules, workplace safety, and consumer protection.
The question is always whether Congress meant to set a floor (states can go above it) or a ceiling (states cannot). Courts look at the statute’s text, structure, and purpose. When a federal law expressly forbids stricter state rules, the federal standard controls in both directions. When it does not, states usually have room to add protections.
When Federal Law Actually Overrides State Law: Preemption
Preemption is how the Supremacy Clause does its work in practice. When Congress legislates within its constitutional authority, that law can displace conflicting state law. Courts sort preemption into two broad kinds.
Express Preemption
Sometimes Congress spells it out. The Employee Retirement Income Security Act (ERISA) states that it “shall supersede any and all State laws insofar as they may now or hereafter relate to any employee benefit plan.”4Office of the Law Revision Counsel. 29 USC 1144 – Other Laws With language that clear, states cannot build their own regulatory framework for covered employee benefit plans.
Implied Preemption
More often Congress is silent, and courts infer preemptive intent from how the federal scheme is built. Field preemption applies when federal regulation is so comprehensive that Congress plainly meant to occupy the whole area, leaving no room for state legislation. Immigration and airline pricing, routes, and services are longstanding examples. Conflict preemption is narrower: it applies when following both laws at once is impossible, or when the state law stands as an obstacle to Congress’s objective. A state cannot require a product label that federal law forbids, because obeying one law means violating the other.
States Do Not Have to Help Enforce Federal Law
Even where federal law clearly applies, the federal government cannot draft state officials to enforce it. The Supreme Court has been building this anti-commandeering rule for more than three decades, and it explains why states can seem to openly resist federal policy without breaking the law.
In New York v. United States (1992), Congress tried to force states to either regulate radioactive waste on federal terms or “take title” to the waste. The Court struck the take-title provision down, holding that “Congress may not commandeer the States’ legislative processes by directly compelling them to enact and enforce a federal regulatory program.”5Law.Cornell.Edu. Anti-Commandeering Doctrine Five years later, Printz v. United States (1997) extended the rule to state executive officers, striking down a Brady Act requirement that local law enforcement conduct handgun background checks. The federal government, the Court said, may neither issue directives requiring states to address particular problems nor command state officers to administer a federal regulatory program.6Law.Cornell.Edu. Printz v United States
Murphy v. NCAA (2018) pushed the doctrine further. A federal law had prohibited states from authorizing sports betting. The Court struck it down, holding that “the distinction between compelling a State to enact legislation and prohibiting a State from enacting new laws is an empty one.”7Supreme Court of the United States. Murphy v National Collegiate Athletic Association Congress cannot direct state legislatures in either direction.
The practical consequence: when Washington wants a federal law enforced across the country, it has to use federal personnel and federal money. State police, state agencies, and state legislators cannot be pressed into service.
The Federal Government’s Workaround: Strings on Money
Washington cannot order states around, but it can pay them to comply. Congress routinely attaches conditions to federal funds — take the money, take the rules — and that is its most effective lever over state policy.
The national drinking age is the classic case. The Twenty-First Amendment gives states authority over alcohol, so Congress could not simply set a nationwide age. Instead, it directed the Secretary of Transportation to withhold a percentage of federal highway money from any state that let people under 21 buy or publicly possess alcohol.8Office of the Law Revision Counsel. 23 USC 158 – National Minimum Drinking Age Noncompliant states currently lose 8% of their federal highway funding. Every state raised its drinking age.
The Supreme Court blessed the technique in South Dakota v. Dole (1987), on the conditions that Congress state the terms clearly, tie them to a federal interest, and stop short of financial pressure so severe it becomes coercion.9Justia U.S. Supreme Court Center. South Dakota v Dole, 483 US 203 (1987) That coercion limit is not theoretical. In NFIB v. Sebelius (2012), the Court found that the Affordable Care Act’s threat to strip states of all existing Medicaid funding — around 10% of a typical state’s entire budget — if they refused to expand coverage crossed the line. Congress could withhold new expansion money from holdouts, but not their existing Medicaid dollars.10Legal Information Institute. National Federation of Independent Business v Sebelius (2012) Losing 8% of highway funds is a nudge. Losing an entire Medicaid budget is compulsion.
Marijuana and Sanctuary Policies
Two current standoffs show how these rules operate together.
Marijuana remains a Schedule I controlled substance under federal law. As of late 2025, a rulemaking process to reschedule it to Schedule III was still pending an administrative hearing and had not been finalized.11The White House. Increasing Medical Marijuana and Cannabidiol Research Meanwhile, 24 states and Washington, D.C. have legalized recreational use, and more allow medical use. The Supremacy Clause means federal law technically still applies everywhere, and Gonzales v. Raich (2005) confirmed Congress’s authority reaches even marijuana grown and consumed inside a single state. But anti-commandeering means the DEA cannot make state or local police enforce the federal ban. If federal agents want to shut down a state-licensed dispensary, they have to do it themselves. Congress has also barred the Justice Department from spending funds to prosecute state-legal medical marijuana activity, a restriction renewed through annual spending bills.
Immigration works on the same logic. Cities and states that limit local cooperation with federal immigration authorities rely on anti-commandeering: federal courts have held that immigration detainer requests are voluntary, and that requiring local jails to hold people for federal agents would commandeer state resources for a federal program. Federal agencies can still enforce immigration law themselves. A 2025 federal decision involving Illinois reaffirmed that state laws limiting cooperation on detainers fall within anti-commandeering protection.
Can a State Simply Refuse to Follow Federal Law?
No — not through any legally recognized mechanism. The idea that a state can “nullify” a federal law inside its borders goes back to the Kentucky Resolutions of 1798, and the Supreme Court has rejected it every time it has surfaced, from McCulloch v. Maryland through Cooper v. Aaron (1958) and beyond. No state has the authority to declare a federal law void.
What states can do is decline to help enforce it, and that refusal is constitutionally protected. There is a real difference between saying “we will not spend state resources enforcing your law” (legal) and saying “your law does not apply here” (not legal). Marijuana and sanctuary policies fall into the first category. States are not nullifying federal drug or immigration law; they are simply refusing to enforce it with state personnel, and the federal government remains free to enforce those laws on its own.
So the answer to whether states have to follow federal laws is layered but consistent. Valid federal law wins any real conflict. Congress cannot legislate outside its constitutional powers. Where it has power, it often sets a floor states can exceed. And even when a federal law clearly applies, Washington has to enforce it with its own hands.