brewer-jan-arizona-rtr2eq0n

Arizona Gov. Jan Brewer calls the Obama administration's lawsuit a "massive waste of taxpayer funds." ((Kevin Lamarque/Reuters))

The U.S. government sued Arizona on Tuesday to throw out the state's toughest-in-the-nation immigration law and keep other states from copying it.

The lawsuit filed in federal court in Phoenix said the law, due to take effect July 29, usurps the federal government's "pre-eminent authority" under the constitution to regulate immigration.

The move sets the stage for a high-stakes legal clash over states' rights at a time when politicians in some other states have indicated they want to follow Arizona's lead.

The legal action represents a stern denunciation of the law, which the Justice Department declared will "cause the detention and harassment of authorized visitors, immigrants and citizens who do not have or carry identification documents" while ignoring "humanitarian concerns" and harming diplomatic relations.

Supporters of the law said the lawsuit was unnecessary and blamed the federal government for neglecting problems at the border for years. Arizona Gov. Jan Brewer called the complaint "a terribly bad decision" and defended the law as "reasonable and constitutional."

Arizona passed the measure after years of frustration with illegal immigration, including drug trafficking, kidnappings and murders. The state is the biggest gateway into the U.S. for illegal immigration, and it's home to an estimated 460,000 illegal immigrants.

The law requires police, while enforcing other laws, to question a person's immigration status if there's reasonable suspicion that the person is in the country illegally. It also requires legal immigrants to carry their immigration documents and bans day labourers and people who seek their services from blocking traffic on streets.

Other states have said they want to take similar action — a scenario the Obama administration cited as a reason for bringing the lawsuit.

"The Constitution and the federal immigration laws do not permit the development of a patchwork of state and local immigration policies throughout the country," the lawsuit says.

The legal arguments focus on the constitution's assertion that federal laws override state laws. The lawsuit says that comprehensive federal laws already on the books cover illegal immigration — and that those statutes take precedence.

"In our constitutional system, the federal government has pre-eminent authority to regulate immigration matters," the lawsuit says. "This authority derives from the United States Constitution and numerous acts of Congress. The nation's immigration laws reflect a careful and considered balance of national law enforcement, foreign relations, and humanitarian interests."

The lawsuit also says that the Arizona measure will impose a huge burden on U.S. agencies in charge of enforcing immigration laws, "diverting resources and attention from the dangerous aliens who the federal government targets as its top enforcement priority."

The next step is for the case to be assigned a judge, who will decide whether to grant a preliminary injunction to temporarily block the law from taking effect. Brewer predicted that the law would survive the federal challenge as well as pending suits previously filed by private groups and individuals.

"As a direct result of failed and inconsistent federal enforcement, Arizona is under attack from violent Mexican drug and immigrant smuggling cartels. Now, Arizona is under attack in federal court from President Obama and his Department of Justice," Brewer said.

"Today's filing is nothing more than a massive waste of taxpayer funds."