After a long legal battle the ACLU, on behalf of plaintiffs in Lopez Valenzuela v. Maricopa County prevailed by blocking further implementation of a law that for years did not allow judges to even consider bail for criminal defendants who were suspected of having "entered or remained in the United States illegally," and which applied to most state felony charges in Arizona, including relatively minor crimes such as shoplifting and possessing a phony ID. As a result of Proposition 100, which amended the state constitution, state courts were required to jail countless individuals who posed no risk of flight or danger to others.

Over the last two years since the "show me your papers" provision of Arizona's anti-immigrant law SB 1070 went into effect, the ACLU has documented numerous cases of racial profiling and illegal detentions by law enforcement officials throughout the state. In Tucson alone, the ACLU has filed several "Notices of Claim" alleging that law enforcement officers regularly engage in racial profiling and illegal detention as a result of applying the law.

The American Civil Liberties Union, ACLU of Arizona, and private firm Aiken Schenk Hawkins & Ricciardi P.C., have settled a federal lawsuit challenging an unconstitutional municipal ordinance that pressures landlords to evict a tenant if more than four calls to police are placed in 30 days or for crimes occurring at the property, even when the tenant is the victim.

(Formerly Friendly House et al. v. Whiting). The U.S. Supreme Court has upheld the most hotly disputed part of Arizona's anti-immigrant law, S.B. 1070, which requires police to determine the immigration status of someone arrested or detained when there is "reasonable suspicion" they are not in the U.S. legally. The ACLU, along with a coalition of civil rights organizations, will continue to challenge the Arizona law on other constitutional grounds.