United States v. State of Iowa, 126 F.4th 1334

Iowa enacted Senate File 2340, criminalizing the presence of previously deported aliens within Iowa and mandating state-level removal orders.
The law prohibits judges from staying prosecution due to pending or potential federal immigration decisions.
The United States challenged the law as facially invalid, seeking a preliminary injunction, arguing the law is preempted by federal immigration authority.
The district court granted the injunction, finding likely preemption under the Supremacy Clause, and that the U.S. would face irreparable harm if the law took effect.
Iowa appealed the grant of the preliminary injunction to the Eighth Circuit, which affirmed the district court’s order.

Issue	Plaintiff's Argument	Defendant's Argument	Held
Standing	U.S. suffers concrete, particularized, and imminent injury to its immigration enforcement interests	Injuries are speculative; law not yet enforced	U.S. has standing—injury is particularized, imminent, traceable, and redressable
Cause of Action	Equitable tradition allows U.S. to sue to enjoin unconstitutional state actions	No implied cause of action under Supremacy Clause; equity must be grounded in tradition	Cause of action recognized for U.S. to seek injunctive relief against state action violating federal law
Preemption / Merits	Iowa’s Act conflicts with federal immigration law by creating state penalties and mandatory removal, undermining federal discretion and foreign policy	Law can be interpreted to mirror federal law and discretionary stays; does not actually regulate removal beyond state	The Act is conflict-preempted: it stands as an obstacle to congressional purposes and federal discretion over immigration enforcement
Preliminary Injunction Factors	Irreparable harm to U.S. interests, balance of equities favors injunction, high likelihood of success, public interest supports enjoining law	State harmed if unable to enforce law; public interest in state enforcement	All factors favor injunction; no abuse of discretion by district court

Arizona v. United States, 567 U.S. 387 (Supreme Court found state immigration enforcement laws preempted by federal law, emphasizing federal control over immigration policy)
Crosby v. National Foreign Trade Council, 530 U.S. 363 (Supreme Court explained the standard for conflict preemption and effects-based analysis)
Geier v. American Honda Motor Co., Inc., 529 U.S. 861 (Articulated the approach to conflict preemption and reconciliation of federal and state laws)
Hines v. Davidowitz, 312 U.S. 52 (Established that state immigration laws can be preempted due to federal government’s primacy in foreign affairs and immigration)
INS v. Aguirre-Aguirre, 526 U.S. 415 (Recognized broad discretion granted to federal immigration officials)
Mutual Pharmaceutical Co., Inc. v. Bartlett, 570 U.S. 472 (Clarified that state laws in conflict with federal law are without effect)
Mayor, Aldermen and Commonality of the City of New York v. Miln, 36 U.S. 102 (Even state police powers are subject to federal preemption in immigration matters)