The case involves a legal challenge to Arizona’s controversial S.B. 1070, also known as the “Support Our Law Enforcement and Safe Neighborhoods Act.” This law aimed to empower local law enforcement to enforce federal immigration laws, including detaining and arresting individuals suspected of being undocumented. The United States government filed a lawsuit arguing that S.B. 1070 was preempted by federal law, as immigration regulation is a federal responsibility. The case focused on whether state-level enforcement measures like S.B. 1070 could legally supplement federal immigration policies, especially when those state actions conflicted with established federal guidelines.

Amici curiae, including the League of United Latin American Citizens (LULAC) and the National Coalition of Latino Clergy and Christian Leaders, supported the government’s stance, highlighting how the law led to unconstitutional detentions and arrests of individuals whose presence in the U.S. was authorized under federal law but who did not possess formal documentation. The district court granted a preliminary injunction against key provisions of S.B. 1070, which included mandatory immigration status checks during stops, criminalizing the failure to carry registration documents, and creating new state-level crimes related to unauthorized work. The decision emphasized the federal government’s exclusive authority over immigration matters and the risks of conflicting state and federal enforcement efforts.