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PHOENIX -- A referendum drive and a lawsuit have emerged as potential road blocks to Arizona's tough new law on illegal immigration that has thrust the state into the national spotlight.

The legal action set to be filed Thursday in federal court is aimed a preventing enforcement of the controversial measure, while the ballot question could put it on hold until 2012.

Signed last week by Republican Gov. Jan Brewer, the law requires local and state law enforcement to question people about their immigration status if there's reason to suspect they're in the country illegally, and makes it a state crime to be in the United States illegally.

A draft of the proposed lawsuit obtained by The Associated Press shows the National Coalition of Latino Clergy and Christian Leaders will seek an injunction preventing authorities from enforcing the law. The group argues federal law pre-empts state regulation of national borders, and that Arizona's law violates due-process rights by allowing suspected illegal immigrants to be detained before they're convicted.

Other Hispanic and civil rights groups, including the American Civil Liberties Union and the Mexican American Legal Defense and Educational Fund, are also planning lawsuits. And U.S. Attorney General Eric Holder has said the federal government may challenge the law.

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On Wednesday, a group filed papers to launch a referendum drive that could put the law on hold until 2012 if organizers wait until the last minute to turn in petition signatures needed to get the measure on the ballot.

Opponents of the law have until late July or early August to file the more than 76,000 signatures -- the same time the law is set to go into effect. If they get enough signatures, the law would be delayed until a vote.

But the deadline to put a question on the November ballot is July 1, and a referendum filing later than that could delay a vote on the law until 2012, officials with the Secretary of State's Office said.

"That would be a pretty big advantage" to the law's opponents, said Andrew Chavez, head of a Phoenix-based petition-circulating firm and chairman of the One Arizona referendum campaign.

The legislation's chief sponsor, Republican Rep. Russell Pearce, said he has no doubt voters will support the new law at the ballot box, which would then protect it from repeal by the Legislature. In Arizona, measures approved by voters can only be repealed at the ballot box.

The clergy group's lawsuit targets a provision allowing police to arrest illegal-immigrant day laborers seeking work on the street or anyone trying to hire them, according to the draft. It says the solicitation of work is protected by the First Amendment.

State Rep. Ben Miranda, a Phoenix Democrat who will serve as the local attorney on the case, said it was important to file the suit quickly to show local Latinos and the rest of the country that there's still a chance the law won't be enacted.

"I think there's real damage being caused right now," Miranda said. "How do you measure the kind of fear ... going on in many parts of this community?"

At least three Arizona cities also are considering lawsuits to block the law. Phoenix Mayor Phil Gordon said the measure would be "economically devastating," and called on the City Council to sue the state to stop it from taking effect.

The council rejected that idea Tuesday, yet the mayor told reporters he retained legal counsel to prepare a lawsuit to file on behalf of the city.

Tucson leaders also are considering their options to block the law, and Flagstaff City Councilman Rick Swanson said the city had a duty to protect its residents who might be targeted.

Meanwhile, the effect of the law continued to ripple beyond Arizona.

A Republican Texas lawmaker said she'll introduce a measure similar to the Arizona law next year. Texas Rep. Debbie Riddle of Tomball said she will push for the law in the January legislative session, according to Wednesday's editions of the San Antonio Express-News and Houston Chronicle.

And Republicans running for governor in Colorado and Minnesota expressed support for the crackdown. "I'd do something very similar" if elected," Former Rep. Scott McInnis, told KHOW-AM radio in Denver.