Arizona's immigration law is set to go into effect at the end of this month. The law requires police -- who are enforcing other laws -- to question a person's immigration status, if there's rationale suspicion they are in this country illegally.
It also makes it a crime for legal immigrants not to carry their immigration documents. The law launched a flurry of protests around the nation.
On Tuesday, the Justice Department filed suit, saying the law violates the Constitution. The suit says, "The federal government has pre-eminent authority to regulate immigration matters."
"Congress cannot delegate that authority to the states and the states cannot take that authority unto themselves," says Hector Villagra from the ACLU.
The government is seeking an injunction to delay the July 29 implementation of the Arizona law until the case is resolved, but at least one Arizona sheriff is defiant in his response.
"As far as this sheriff is concerned, lawsuits or no lawsuits, I'm going to continue enforcing the federal and state immigration laws," says Maricopa County Sheriff Joe Arpaio.
San Francisco police Chief George Gascon spent three years as chief in Mesa, Arizona. He opposes the Arizona law and is glad to see it challenged.
"I'm not sure that you can operate under the umbrella of SB 1070 and do so in a Constitutional fashion. In looking at some of the training that's being developed for Arizona police officers, I see tremendous problems," says Gascon.
But an Arizona attorney who successfully fought challenges to other Arizona immigration laws, believes the law will be upheld. And he questioned the Obama administration's motivation.
"The federal government by its lawsuit today says it cares more about its relationship with Mexico than its relationship with Arizona" says attorney Andrew Thomas.
ABC7's legal analyst Dean Johnson thinks that Arizona law may be struck down. He says courts have repeatedly ruled many immigration laws, passed by state and local governments, are unconstitutional and that national policy based on immigration must be uniform.