United States v. State of Iowa, 737 F.Supp.3d 725

Iowa enacted Senate File 2340 (SF 2340), which criminalizes certain immigration-related offenses and empowers state court judges to order noncitizens to return to their countries of origin.
Plaintiffs (the United States and Iowa Migrant Movement for Justice with individual members) sought a preliminary injunction against enforcement, arguing federal law preempts state action.
SF 2340 would, among other things, penalize individuals present in Iowa who have ever been subject to denial of admission, exclusion, deportation, or removal from the U.S, even if now lawfully present.
The law requires state criminal prosecutions and judicial removal orders, and bars suspension of prosecutions due to pending federal immigration proceedings.
Federal officials argued SF 2340 would undermine federal immigration procedures, harm foreign relations, and risk violations of international treaties.
The court considered whether both the United States and the organizational plaintiffs had standing, and analyzed whether a preliminary injunction was warranted under established multi-factor tests.

Issue	Plaintiff's Argument	Defendant's Argument	Held
Whether plaintiffs have standing to challenge SF 2340	Plaintiffs' members face credible risk of prosecution and organizational resources are diverted.	The law doesn't apply to lawful residents; harm is speculative/self-inflicted.	Court holds both individual and organizational standing established.
Whether the United States has a cause of action to seek preemption under Supremacy Clause	Equity permits the U.S. to sue to enjoin preempted state law.	Supremacy Clause does not create an independent cause of action (relying on Armstrong).	Court holds the U.S. can sue in equity for preemption (consistent with precedent).
Whether SF 2340 is preempted by federal immigration law (field/conflict preemption)	SF 2340 intrudes into federal domain, criminalizing conduct Congress regulates exclusively.	Argues state law mirrors federal law/only supplements enforcement.	SF 2340 is preempted by federal law both by field and conflict preemption.
Whether the preliminary injunction standards are met (Dataphase factors)	Enforcement would cause irreparable harm by exposing lawful residents to prosecution, undermining federal law, and damaging foreign relations.	Argues no irreparable harm and state has enforcement interests.	Threat of irreparable harm exists; balance and public interest support injunction.

Arizona v. United States, 567 U.S. 387 (2012) (federal immigration law preempts state efforts to regulate in the immigration field)
Armstrong v. Exceptional Child Center, Inc., 575 U.S. 320 (2015) (limitations of Supremacy Clause as a cause of action)
Hines v. Davidowitz, 312 U.S. 52 (1941) (states are preempted in areas where Congress intended a unified federal voice in foreign affairs)
DeCanas v. Bica, 424 U.S. 351 (1976) (Congress can preempt state law in the realm of immigration)
Rice v. Santa Fe Elevator Corp., 331 U.S. 218 (1947) (field preemption where federal regulation is pervasive)
Babbitt v. United Farm Workers Nat. Union, 442 U.S. 289 (1979) (standing exists where threat of prosecution is credible, even absent enforcement history)