A federal judge in the United States has blocked parts of a strict new immigration bill passed by the state of Arizona, a day before it was to take effect.
The American Civil Liberties Union, which filed the challenge, argued that the law impinged on the right of the federal government to determine immigration law.
In a temporary injunction, US District Judge Susan Bolton blocked a requirement that police check the immigration status of criminal suspects whom they had stopped while enforcing other laws.
The federal government argued the law usurped its authority over immigration policy.
Among the other parts of the law blocked was a section making it a crime not to carry immigration papers.
The Arizona legislature passed the law in April amid fears of rising crime caused by illegal aliens and complaints the federal government had failed to act on the matter.
Governor Jan Brewer pledged to appeal against the ruling.