Gonzalez and ten other people of Mexican descent (plaintiffs) sued the City of Peoria, Arizona and some of its police officers and public officials for unlawful arrests and detentions in violation of the Fourth and Fourteenth amendments to the United States Constitution and the Civil Rights Act of 1871. The plaintiffs claim that the city adopted policies which encouraged police officers to detain people of Mexican descent solely based on their appearance. People who did not have valid immigration documentation or identification were released to immigration authorities. The plaintiffs also claim that under the doctrine of preemption state and local police officers are precluded from enforcing immigration laws. The Court of Appeals for the Ninth Circuit reviewed the case on the government’s appeal.