What are the main legal foundations and Supreme Court precedents affecting sanctuary city policies?
Executive summary
Sanctuary-city law sits at the intersection of federal plenary power over immigration and constitutional limits on federal coercion of the states, producing a body of doctrine anchored in the Supremacy Clause, the Spending Clause, and the Tenth Amendment’s anti-commandeering principle [1] [2] [3]. Recent litigation—most notably challenges to Trump-era funding conditions and executive orders—has reinforced that the federal government cannot broadly compel or coerce localities to enforce federal immigration law, though questions of preemption, information-sharing statutes, and the Supreme Court’s changing composition keep the issue unsettled [4] [5] [6] [7].
1. Federal plenary power and preemption: who owns immigration?
The federal government has long been recognized as holding plenary authority over immigration—entry, removal, and naturalization derive from Article I powers and have been repeatedly described as primarily federal functions—so state laws that directly regulate immigration can be preempted under the Supremacy Clause [1] [6]. But courts and scholars stress this does not automatically make every local sanctuary policy invalid: preemption requires that a federal statute either expressly or implicitly displace state law, and courts have found Section 1373’s narrow information-sharing mandate does not by itself preempt many local policies governing custody, release dates, or contact information [6].
2. Anti-commandeering: the constitutional wall against federal coercion
A decisive legal bulwark for sanctuary jurisdictions is the Tenth Amendment anti-commandeering doctrine—established across multiple precedents and invoked repeatedly in sanctuary litigation—which bars the federal government from forcing state and local officials to administer or enforce federal regulatory programs, including immigration enforcement [3] [8]. Courts have applied that principle to strike down or block attempts to condition broad categories of federal grants on compliance with federal immigration enforcement demands, treating coercive funding conditions as unconstitutional compulsion [8] [2].
3. Spending Clause limits: the Dole test and funding conditions
Supreme Court precedent on conditional federal spending requires that any conditions on grants be unambiguous, related to the federal program’s purpose, and not coercive in practice—a test rooted in the Court’s spending-power jurisprudence that lower courts used to block Trump administration efforts to withhold law-enforcement grants from sanctuary jurisdictions [9] [2] [4]. Multiple federal courts found DOJ and executive orders exceeded those limits, and several appellate rulings invalidated the administration’s grant conditions before the Supreme Court ultimately dismissed related petitions when parties settled or withdrew appeals [4] [5].
4. Statutory tools: Sections 1373 and 1644 and their contested reach
Congressional statutes like 8 U.S.C. §1373 and §1644 figure centrally but ambiguously: they bar certain restrictions on sharing immigration-status information, yet courts have disagreed about whether those provisions preempt or displace local limits on cooperation, with several decisions concluding the statutes do not clearly cover custody or release-date information and therefore do not automatically nullify sanctuary ordinances [6] [1]. That statutory uncertainty is a recurring flashpoint because administrations can attempt to invoke the statutes to justify denial of funds or other penalties—a strategy courts have pushed back on when the link between the statute and a funding condition is tenuous [6] [2].
5. Key litigation and the shifting stakes
San Francisco v. Trump and related suits produced substantial victories for sanctuary jurisdictions in district and circuit courts and led to the DOJ dropping appeals and the Supreme Court dismissing petitions, effectively leaving lower-court rulings that limited the executive’s power to penalize sanctuary policies in place—though not as definitive, nationwide Supreme Court precedent [4] [5]. Recent rounds of litigation—including the administration’s renewed executive orders and suits against Chicago and others—illustrate that the issue keeps circulating through the courts, intensified by political motives to use funding threats as leverage [10] [11].
6. What might change: the Court, doctrine, and political aims
Legal analysts warn that changes in the Supreme Court’s composition and the political imperative to control immigration enforcement could prompt the high court to revisit anti-commandeering, spending-power limits, and preemption doctrines that have favored sanctuary jurisdictions—meaning precedents that sanctuary advocates have relied upon may not be immutable [7]. For now, however, the dominant legal foundations protecting sanctuary policies are the anti-commandeering principle, limits on coercive spending conditions, and narrow readings of federal statutes like §1373—and those remain the principal battlegrounds in pending and future litigation [8] [2] [6].