Flashpoints of State-Federal Cooperation in Immigration Enforcement—Part II: Local Immigration Arrests & Detentions

(first published July 2, 2026 at https://andersnewbury.substack.com)

The first segment of this series on local involvement in immigration enforcement examined the legal and practical implications of so-called “sanctuary” jurisdictions. This segment examines the legal repercussions, in Montana and elsewhere, of local cooperation in the crux of the deportation system: arrests and detentions.

Immigration Arrest Authority and 287(g) Agreements

In contrast to so-called “sanctuary” jurisdictions seeking to avoid being shanghaied into federal enforcement efforts, other polities that are more supportive of aggressive deportations have actively sought opportunities to commit their own resources to the project.[1] But the U.S. Supreme Court has ruled that state and local governments are generally prohibited from taking action in immigration enforcement on their own initiative.[2] One exception is found in section 287(g) of the Immigration and Nationalization Act, which allows state and local law enforcement to enter into a formal agreement with federal authorities and undergo required training, ultimately becoming deputized federal immigration agents.

Recently, the federal government has offered substantial financial incentives to local law enforcement willing to enter these agreements. This program has raised concern not only of local law enforcement becoming distracted from actually fighting crime, but also of further undercutting public safety by diminishing the undocumented community’s willingness to report crimes to local police.

In Montana, Republican Attorney General Austin Knudsen entered a 287(g) agreement to authorize Montana’s Highway Patrol and Department of Criminal Investigation to “work hand in hand” with federal authorities. The extent to which the Patrol has in fact been involved in actual immigration enforcement activities, however, remains unclear.

At the local level, Montana law enforcement involvement in immigration operations has been sporadic. The Belgrade police department appears to have assisted in a federal immigration raid: absent a 287(g) agreement, the source of legal authority for Belgrade to have done so appears dubious. Other jurisdictions, such as the Flathead County Sheriff’s office and Hardin Police Department have denied involvement in federal immigration enforcement activities in the area.

Local Prison/Jail Space:

One major bottleneck in the Trump Administration’s deportation efforts has been finding the bed space to put detainees awaiting deportation proceedings. Focusing enforcement on those already residing in the country, rather than on apprehending border crossers, has increased the time it takes to deport individuals, as residents suspected to be unauthorized are put on a slower procedural deportation track. As a result, demand for detention space has grown rapidly.

Despite having already spent over a billion dollars on controversial efforts to turn warehouses into detention centers, the Trump Administration is relying heavily on contractual intergovernmental agreements with hundreds of local and state-run facilities to house federal immigration detainees.[3] Such agreements have become important income streams for many localities.[4] Opponents to these agreements point to preexisting overcrowding plaguing many local jails, lapses in accountability for conditions of confinement, and due process concerns when prisoners are unable to be located by friends or family and are held for lengthy periods of time incommunicado, without proper access to the courts.[5]

Local residents are often unaware that local or state facilities are being used to house federal immigration detainees. In Vermont, for example, lawmakers were concerned to discover that, despite the State’s general reluctance to be involved in federal immigration enforcement, the state Department of Corrections had been operating under a longstanding agreement to house federal immigration detainees pursuant to a bed-renting contract. In Montana, the Cascade County detention center—amidst chronic jail overcrowding problems—contracts to hold ICE detainees to the tune of $115 per detainee per day (more than double what state detainees bring in). The 287(g) agreements described above are often implicated in these bed-renting agreements. Gallatin and Flathead County have 287(g) agreements; Yellowstone County does not—citing its already chronically-crowded jail space.

Immigration Detainers:

A particularly controversial piece of local-federal immigration enforcement cooperation is something referred to as an immigration “detainer.” Under an Obama-era database sharing program, an individual being held by local or state authorities—usually in the form of a brief post-arrest detention—on the basis of an alleged state law violation might be flagged in the federal immigration database as subject to removal. Federal authorities then send a document, referred to as a “detainer,” to the local law enforcement, asking that (a) federal immigration authorities be notified before the individual was slated to be released from state or local custody and (b) that the individual be held for up to 48 additional hours beyond that scheduled release time. Local compliance with these requests facilitates federal immigration officers’ ability to arrive and easily take into custody a removeable individual who happens to have made contact with the state criminal justice system in some way.

From a legal perspective, however, this extra 48 hours poses a serious problem. Because it involves holding someone behind bars beyond when the individual otherwise should have be released, an officer complying with a detainer technically makes a “new arrest” for Fourth Amendment purposes. [6] Courts—including the Montana Supreme Court—have therefore found detainer compliance illegal unless the local law enforcement has some express authority to make a new immigration arrest, such as a 287(g) agreement discussed above.

One creative effort to get around such rulings was to overlay preexisting federal bed-renting contracts on top of a detainer request. Federal authorities assured reticent local detention centers that the contract evaded the “new arrest” problem with the following legal sleight of hand: the bed-renting agreement converts the local jail cell into a “federal” facility, so local jailors aren’t actually the ones holding prisoners beyond their lawful release date—the feds are. During the first Trump Administration, I authored a law review article examining this practice in Vermont, concluding that the underlying legal theory was dubious at best. That same year, a Minnesota Court rejected a similar argument made by a local sheriff attempting to comply with ICE detainers.[7]

As noted in the previous segment of this series, the second Trump Administration has ratcheted up the intensity on the detainer debate even further by declaring failure to comply with detainer requests sufficient to land state or local jurisdiction on the so-called “sanctuary jurisdiction” list, there to be singled out for the Administration’s ire. This puts many jurisdictions in the unenviable position of choosing between risking liability by complying with an illegal detainer or facing potential Presidential retribution for refusing to do so.

Conclusion

Local and state-level involvement in arresting and detaining potentially removeable individuals powers much of President Trump’s deportation machine. But these efforts are subject to significant legal constraints and often operate with dubious legality. And yet, the public is often unaware that their state and local law enforcement resources are being expended on supporting federal immigration enforcement efforts, even as local facilities reach capacity and state defendants are shipped to out of state private prisons. The next segment in this series will examine the enforcement engine’s most widespread and—from the perspective of a society which has historically struggled to achieve race-neutral policing—often troubling manifestation: the traffic stop.

[1] See, e.g., United States v. Arizona, 567 U.S. 387, 408 (2012).

[2] Arizona, 567 U.S. at 408.

[3] Ellyn Jameson, Ice Detention Through U.S. Marshals Agreements, 35 Geo. Immigr. L.J. 279, 284 (2020) (compiling list of 425 facilities with publicly available Intergovernmental Agreement with federal U.S. Marshalls Service; ICE listed as an authorized user on 244); Anders Newbury, Illegal Immigration Arrests: A Vermont Perspective on State Law and Immigration Detainers Supported by Intergovernmental Agreements, 44 Vt. L. Rev. 645 (2020), https://lawreview.vermontlaw.edu/wp-content/uploads/2020/06/07-Newbury.pdf.

[4] Jameson, supra n. 3 at 293–94.

[5] Id. at 301 (noting lax USMS inspections, 158 deaths in USMS custody from June 2016 to June 2019).

[6] Ben Levey, Disrupting the Jail-to-Deportation Pipeline in Wisconsin, 2023 Wis. L. Rev. 2027, 2037, 2068 (2023); Ramon v. Short, 460 P.3d 867, 879 (Mont. 2020); Lunn v. Commonwealth, 78 N.E.3d 1143, 1160 (Mass. 2017); Kate Evans, Immigration Detainers, Local Discretion, and State Law’s Historical Constraints, 84 Brook. L. Rev. 1085 (2019); Sean Turley, Death by Fifty Cuts: Exporting Lunn v. Commonwealth to Maine and the Prospects for Waging a Frontal Assault on the ICE Detainer System in State Courts, 70 Me. L. Rev. 235 (2018); Newbury, supra n. 3.

[7] Esparza v. Nobles County, #53-CV-18-751 (MN 5th Jud. Dist. Ct.); see also Jameson, supra n. 3.