When U.S. Immigration and Customs Enforcement (ICE) determines that an individual held in state or local custody may be removed from the United States, it commonly issues an immigration detainer. Detainers inform local law enforcement agencies (LLEAs) of ICE’s intent to assume custody and request notice before any release. Controversially, they also request LLEAs to “maintain custody . . . for a period not to exceed 48 hours beyond the time [an individual] . . . would otherwise have been released.” Detainers cannot compel unwilling LLEAs to hold individuals otherwise eligible for release, nor can LLEAs, on their own initiative, detain individuals solely due to suspected removability. What is less clear is whether ICE detainers enable willing LLEAs to maintain custody over individuals when other bases for detention have lapsed. Though ICE routinely asks LLEAs to do just that, a series of federal court decisions have questioned LLEA compliance on statutory and constitutional grounds. Recently, in Lunn v. Commonwealth, the Massachusetts Supreme Judicial Court took a different approach, holding that state law enforcement lacked authority to detain individuals subject to ICE detainers under state law. Lunn is the first ruling by a state’s highest court addressing ICE detainer compliance and, because of its grounding in Massachusetts law, seems to offer few lessons beyond the state’s borders. However, by enforcing the long-standing common law limits on warrantless arrest authority underlying the Fourth Amendment, Lunn found a state law mechanism for addressing the constitutional concerns raised by ICE detainers while avoiding thorny questions of how Fourth Amendment protections and federal sovereignty principles play out in the immigration context.

Massachusetts prosecutors arraigned Sreynuon Lunn on one count of unarmed robbery in Boston on October 24, 2016. Having failed to post bail, Lunn was held in jail until February 6, 2017, when he was brought to court for trial. When Massachusetts proved unready to make its case, the judge dismissed the charge for lack of prosecution. With no criminal charges pending, Lunn would ordinarily have been released. However, having learned that Lunn was subject to an ICE detainer, the judge declined to release Lunn. Hours later, ICE officers arrived at the courthouse and arrested him.

The next morning, Lunn’s lawyer filed an emergency petition with Justice Lenk of the Massachusetts Supreme Judicial Court challenging the municipal court’s authority to hold Lunn. Because Lunn was by then in ICE custody, the issue was already moot; however, “recognizing the important, recurring, and time-sensitive legal issues” ICE detainers raised, Justice Lenk nonetheless raised the case with the full court. In the ensuing litigation, Massachusetts and the Suffolk County Sherriff disclaimed authority to detain individuals subject to ICE detainers, siding with Lunn to argue that compliance with such requests was unauthorized by state law and “raise[d] serious constitutional concerns.” Stepping in to defend ICE detainers, the United States as amicus curiae argued that history and constitutional structure confirmed LLEAs’ “inherent authority” to cooperate with the federal government in enforcing immigration law.

In a per curiam opinion, the court held that Massachusetts law enforcement lacked authority under state law to detain individuals solely on the basis of ICE detainers. It first determined that the detainer at issue was civil in nature, as it related to removal proceedings rather than prosecution. Additionally, the court concluded that under the Immigration and Nationality Act (INA) and the Tenth Amendment, state authorities were not required to comply with ICE detainers.

The court then addressed whether LLEAs could comply with ICE detainers if they so wished. It first determined that Lunn’s continued detention after the criminal charge against him was dropped constituted a new and warrantless arrest. Unconvinced by the United States’ argument that LLEAs possessed “inherent authority” to effect such arrests, the court held that either federal or Massachusetts state law must affirmatively grant that authority. The Court looked to Massachusetts common and statutory law to determine the circumstances under which LLEA officers may make warrantless arrests and found no provision authorizing such arrests for civil immigration violations. Though Massachusetts common law authorized warrantless arrests when an LLEA officer had probable cause to believe someone had committed a felony — or personally witnessed a misdemeanor involving a breach of the peace — the common law did not authorize warrantless arrests for noncriminal offenses. Similarly, while specific Massachusetts statutes authorized warrantless or civil arrests in particular circumstances, no statute authorized such arrests for federal immigration violations. Finally, the court concluded that the INA did not “affirmatively grant[] authority” for LLEAs to make warrantless arrests pursuant to ICE detainers. Moreover, the lack of ordinary procedural safeguards for individuals held on ICE detainers — notably, the absence of a prompt determination of probable cause by a neutral magistrate — counseled against inferring an “inherent” civil arrest authority not clearly specified by state common law or statute.

In holding that Massachusetts law did not authorize warrantless arrests for civil immigration violations, Lunn voiced many of the concerns that have led other courts to conclude that LLEA compliance with ICE detainers violates the Fourth Amendment. However, rulings based in the Fourth Amendment sit in tension with the broad authority over immigration detention that courts have historically afforded the federal government. Whether and to what degree the federal government may assert such authority at the expense of individuals’ constitutional rights — let alone delegate that authority to states — remains a complex and unsettled question of federal law. By instead shifting focus back to the common law constraints on warrantless arrest authority that gave rise to Fourth Amendment guarantees in the first place, Lunn identified a state law framework for protecting rights threatened by ICE detainers.

Several courts have held that warrantless immigration arrests by LLEAs pursuant to ICE detainers — such as the one at issue in Lunn — violate the Fourth Amendment’s guarantee of freedom from “unreasonable searches and seizures” and arrest warrants not backed up by “probable cause.” The amendment’s limits on warrantless arrests have generally been construed in light of common law rules similar to those described in Lunn — and in particular, as a restraint on the authority of law enforcement to make warrantless arrests without probable cause to suspect commission of a felony or misdemeanor. The Supreme Court has also interpreted the Fourth Amendment to require that a neutral magistrate review an officer’s probable cause determination, either before or soon after an arrest. ICE detainers, which ask LLEAs to prolong arrests based only on ICE’s assertions that an individual is civilly removable, therefore offer ample grounds for finding Fourth Amendment deficiencies for much the same reasons that the Lunn court concluded such arrests were unauthorized under common law: the absence of individualized determinations of probable cause or prompt review by a neutral magistrate, and the very use of warrantless arrests for civil offenses.

However, finding that ICE detainers violate the Fourth Amendment would cast doubt on the constitutionality of immigration detention generally, because many of the problems posed by detainers persist after ICE takes custody or when it initiates an arrest on its own. Even if the administrative immigration judges who determine removability are considered neutral, they do not authorize immigration arrest “warrants” or review the subjects of warrantless arrests. The civil nature of federal immigration detention does not obviously justify this deficiency. However, while the Supreme Court has never explicitly addressed whether the federal government’s system of immigration detention passes Fourth Amendment muster, federal power over immigration has always incorporated detention and long operated outside ordinary levels of judicial scrutiny. This broad immigration power supposedly derives from fundamental attributes of sovereignty, rather than affirmative constitutional provisions. Even when the Court showed some willingness to interfere to prevent possibly limitless immigration detention, it couched its intervention in terms of statutory interpretation, rather than its evident constitutional concerns. Courts may therefore worry that deciding that ICE detainers violate the Fourth Amendment would be inconsistent with the historical deference shown to the government in immigration enforcement and would threaten to undermine that enforcement in other contexts.

The basis in sovereignty of enhanced federal immigration arrest and detention authority — if, indeed, such authority exists — thus further complicates any Fourth Amendment detainer analysis. In Arizona v. United States, the Court rejected Justice Scalia’s view of the states as cosovereigns with their own rights to exclude individuals on the basis of immigration status. Instead, the majority determined that Arizona could not unilaterally arrest people who lacked lawful immigration status, even pursuant to a state statute purporting to define a criminal violation under state law. This rejection of sovereignty-based immigration powers for states thus implies that whatever might be the extent of LLEAs’ “inherent authority” to cooperate with federal authorities, such authority is at least constrained by ordinary Fourth Amendment principles. Despite this implication, the Court has historically proved reluctant to allow Fourth Amendment concerns to upset federal immigration enforcement, of which detainers are one facet.

Lunn points a way out of this mess by bringing to the surface the common law restraints on arrest authority through which the Fourth Amendment is understood, particularly with respect to the types of offenses eligible for warrantless arrests. As Lunn makes clear, the constitutionality of ICE detainers matters only if state or federal law authorizes LLEAs to hold individuals on ICE detainers in the first place. And whether or not ICE’s determination that an individual is civilly removable may constitute probable cause for an LLEA arrest, arrests made solely on that basis exceed common law rules of warrantless arrest authority. While many states have statutorily amplified that authority with respect to criminal misdemeanors, states have not, by and large, extended it to civil immigration violations. Whether a state constitutionally could authorize LLEAs to make immigration arrests in cooperation with federal authorities where a federal statute has not done so is an open question — but one that comes up only once a state has tried.

Lunn thus provides a way to address the rights infringed by ICE’s detainer process without deciding a sensitive constitutional question that implicates federal power and sovereignty as much as standard Fourth Amendment principles. Its approach, moreover, gives state political actors the chance in the first instance to determine whether to commit the state’s warrantless arrest authority toward the enforcement of federal immigration laws. Whether or not such a step is constitutional, Lunn was right to conclude that it should not be taken absent explicit state authorization.