Arizona0706The Obama Administration sued Arizona to block the state’s new law cracking down on illegal immigration, setting the stage for a constitutional clash between the federal government and the border state.

Arguing that the law usurps federal authority, the U.S. Justice Department asked a federal court to invalidate Arizona’s requirement that state and local police question and possibly arrest illegal immigrants during the enforcement of other laws, like traffic stops. The lawsuit requests an immediate injunction to delay the July 29 implementation of the law while the case is decided.

Tuesday’s lawsuit has been expected for weeks. President Barack Obama has called the state law misguided. Supporters say it is a reasonable reaction to federal inaction on immigration.

The law requires officers, while enforcing other laws, to question a person’s immigration status if there’s a reasonable suspicion that they are in the country illegally.

Arizona lawmakers passed the measure after years of frustration over problems associated with illegal immigration, including drug trafficking and violent kidnappings. The state is the biggest gateway into the U.S. for illegal immigrants, and is home to an estimated 460,000 illegal immigrants.

President Obama addressed the Arizona law in a speech on immigration reform last week. He touched on one of the major concerns of federal officials, that other states were poised to follow Arizona by crafting their “a patchwork” of immigration enforcement laws.

The law makes it a state crime for legal immigrants to not carry their immigration documents and bans day laborers and people who seek their services from blocking traffic on streets.

The law also prohibits government agencies from having policies that restrict the enforcement of federal immigration law and lets Arizonans file lawsuits against agencies that hinder immigration enforcement.

Kris Kobach, the University of Missouri-Kansas City law professor who helped draft the Arizona law, said he’s not surprised by the Justice Department’s challenge but noted that the law already is being challenged by the American Civil Liberties Union and other groups opposed to the new statute.

“The issue was already teed up in the courts. There’s no reason for the Justice Department to get involved. The Justice Department doesn’t add anything by bringing their own lawsuit,” Kobach said in an interview.

The Associated Press contributed to this report.