The debate over the legality of sanctuary cities is intensifying, with major jurisdictions such as Los Angeles and Chicago instructing their law enforcement officers to resist federal immigration enforcement.
Under current law, the Constitution assigns responsibility for immigration policy to the federal government, with federal immigration law preempting state attempts to enact their own distinct immigration policies. The Constitution grants Congress plenary power over immigration, creating a presumption that federal law should take precedence.
Sanctuary laws exist at state, county, and municipal levels across the country, typically limiting whether and how state or local authorities may cooperate with federal immigration authorities. The California Values Act is one example, prohibiting officials from inquiring into an individual’s immigration status, detaining someone at the request of federal immigration officials (detainers), or providing release date information from local custody.
According to the Center for Immigration Studies, as of January 7, 2025, thirteen states and hundreds of cities and counties had adopted some form of sanctuary laws. In response, at least twelve states passed legislation banning sanctuary policies.
On January 20, 2025, President Trump signed executive orders denying federal funds to “so-called ‘sanctuary’ jurisdictions” that interfere with federal law enforcement. Soon after, the Assistant Attorney General directed prosecutors to investigate state and local officials who resist or obstruct immigration-related commands.
The White House argued that sanctuary policies violate federal statutes on obstruction of justice (18 U.S.C. 1501 et seq.), harboring or hiring illegal aliens (8 U.S.C. 1324), and conspiracy against the United States (18 U.S.C. 371–372). DHS Secretary Kristi Noem warned, “These sanctuary city politicians are endangering Americans and our law enforcement,” while Attorney General Pamela Bondi said such policies “impede law enforcement and put American citizens at risk by design.”
Federal courts have pushed back. On April 24, 2025, a judge blocked the administration from withholding funds from 16 sanctuary jurisdictions. The administration has also filed lawsuits against Illinois, Cook County, and the city of Chicago.
The strongest constitutional argument for sanctuary jurisdictions is the Tenth Amendment’s anti-commandeering doctrine, established in New York v. United States (1992) and Printz v. United States (1997). This principle holds that the federal government cannot compel state or local governments to enforce federal law. As Justice Antonin Scalia wrote in Printz, “The Federal Government may neither issue directives requiring the States to address particular problems, nor command the States’ officers, or those of their political subdivisions, to administer or enforce a federal regulatory program.”
The Trump administration’s attempt to block California’s Values Act failed: the Ninth Circuit upheld the law, the Supreme Court declined review, and similar statutes have been sustained nationwide. Even the conservative Fifth Circuit upheld a Texas law targeting local sanctuary ordinances, ruling that “the Tenth Amendment prevents Congress from compelling Texas municipalities to cooperate in immigration enforcement.”
Immigration detainers further illustrate this principle. Courts have ruled that detainers are requests, not orders. The Third Circuit held that “immigration detainers do not and cannot compel a state or local law enforcement agency to detain suspected aliens.” Any attempt to convert them into mandatory orders would be unconstitutional under the anti-commandeering doctrine. Moreover, keeping individuals jailed after state custody ends violates the Fourth Amendment, which requires a prompt probable cause determination by a magistrate. Both Los Angeles County and New York City have paid millions in settlements for unlawful detentions under immigration detainers.
Funding threats face similar constitutional limits. In NFIB v. Sebelius (2012), the Supreme Court ruled that the federal government cannot attach coercive funding conditions that force state compliance. Denying all or most federal funds to sanctuary jurisdictions to compel immigration enforcement could therefore be unconstitutional.
8 U.S.C. § 1373 provides that “a Federal, State, or local government entity or official may not prohibit, or in any way restrict, any government entity or official from sending to, or receiving from” federal immigration authorities “information regarding the citizenship or immigration status … of any individual.” Critics argue this preempts sanctuary policies, claiming local laws that bar communication with DHS are unlawful. But the statute is narrow: it prevents states from blocking the sharing of immigration status, yet does not require states to collect such information. California’s sanctuary statute, for instance, restricts officials from inquiring into immigration status but does not prohibit sharing it if known. It also bars disclosure of other details, such as release dates, which federal law does not mandate since they are not “information regarding … citizenship or immigration status.”
This debate unfolds against significant enforcement challenges. As of July 21, 2024, ICE’s docket listed 662,566 noncitizens with criminal histories, including 647,572 undocumented individuals without federal supervision. Critics contend sanctuary policies force ICE into more dangerous field arrests instead of custody transfers from jails.
Sanctuary jurisdictions argue the anti-commandeering doctrine protects their refusal to assist federal enforcement. That protection, however, does not extend to active violations of federal law. Under 18 U.S.C. § 1071, it is a felony to harbor or conceal “any person for whose arrest a warrant or process has been issued … so as to prevent his discovery and arrest, after notice or knowledge of the fact that a warrant or process has been issued,” punishable by up to five years in prison for felony warrants.
Similarly, 8 U.S.C. § 1324 criminalizes efforts to “conceal, harbor, or shield from detection” undocumented persons, or to “encourage or induce” illegal entry. In United States v. Hansen, the Supreme Court narrowly interpreted “encourage or induce” to cover only the purposeful solicitation or facilitation of specific acts known to violate federal law. Circuit courts have likewise required affirmative conduct for a harboring conviction, not mere non-cooperation. Thus, the Trump administration would need to prove states are actively harboring criminals, a case it may try to build by pointing to state-issued welcome notices and taxpayer-funded support for undocumented immigrants.
