US judge backs key provision of Arizona migrant law
A US federal judge has ruled Arizona officials can enforce a controversial provision and demand to check the immigration status of suspects.
Critics say the provision, dubbed "show me your papers", will encourage racial profiling.
But lawyers for Arizona's governor argued that police would need "reasonable suspicion" to trigger the demand.
The US Supreme Court has already ruled to uphold the provision.
The headline provision, known as Section 2(B), requires police to make a "reasonable attempt... to determine the immigration status" of anyone who is stopped for another violation.
The Obama administration had challenged the Arizona law, attempting to argue that the Constitution gave the federal government sole authority over immigration policy.
In her ruling, US District Judge Susan Bolton said the court would not ignore the direction from the Supreme Court that the provision could not be further challenged until it had taken effect.
However, as part of a split ruling, she granted a preliminary injunction against a statute making it illegal to transport, harbour or shield individuals suspected of being in the country illegally within Arizona's borders.
The original law was signed by Arizona Republican Governor Jan Brewer in April 2010. She insisted that the federal government was failing to secure the state's border with Mexico.
Arizona is home to an estimated 360,000 undocumented immigrants.
Alabama, Georgia, Indiana, South Carolina and Utah have all adopted variations of the Arizona law.
Immigration has become a key issue as the US edges closer to this year's presidential election.
Mr Obama recently outlined a plan to allow hundreds of thousands of illegal immigrants who came to the US as children the option of legal status and work permits.
Mr Romney has opposed Mr Obama's plan, but has not said how he would address the issue of immigration.