Enlarge By Scott Olson, Getty Images Gary Cozette protests outside Wrigley Field before the start of the Cubs' game against the Arizona Diamondbacks on Thursday in Chicago. Dozens of people demonstrated outside the park calling for a boycott of the series to protest the passage of Arizona's controversial new immigration law.

The first lawsuits in a planned wave of legal challenges to the controversial Arizona immigration law were filed Thursday in Phoenix and Tucson , as a volatile national debate stretched from street protests to the courts.

A new Gallup Poll, meanwhile, shows 39% of Americans support the law, 30% oppose it, and 31% have not heard of it or have no opinion of the measure, which grants police unprecedented authority to question and detain suspected illegal immigrants. The telephone survey of 1,013 adults taken Tuesday and Wednesday has a margin of error of +/–4 percentage points.

A week after the measure was signed into law, a national consortium of Latino churches and a Tucson police officer sued to try to stop it from taking effect. Three other activist groups announced plans to file legal challenges.

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In Phoenix, the National Coalition of Latino Clergy and Christian Leaders said the new law illegally interferes with the federal government's immigration enforcement responsibilities and would spur "racial discrimination."

"This law sanctions police officers to use racial profiling in dealing with the immigrant community," says Miguel Rivera, chairman of the coalition, which represents 300 churches in Arizona.

In Tucson, city patrol officer Martin Escobar charged that provisions for police to question suspects about their immigration status "would seriously impede law enforcement investigations."

University of Texas law professor Sanford Levinson said challengers could make a strong argument that the state overreached because "the feds have exclusive jurisdiction over matters of immigration."

Paul Senseman, a spokesman for Republican Gov. Jan Brewer, who signed the law, said it should stand because it "was designed to mirror existing federal law and to specifically prevent racial profiling."

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The legal challenges were only one front in an emotional debate that reaches far beyond Arizona. Texas state Republican Rep. Debbie Riddle has said she would sponsor a comparable bill to combat illegal immigration in her state; support for a similar bill surfaced in Oklahoma. Elsewhere on Thursday:

• The Denver public school system banned work-related travel to Arizona to protest the law.

• Opponents of the law in Chicago protested at Wrigley Field, where the Arizona Diamondbacks opened a series with the hometown Cubs.

• In Washington, Senate Democratic leaders unveiled a proposal that, in part, would add federal agents to the Southwestern border. President Obama called it "a very important step in the process of fixing our nation's broken immigration system."

• Colombian singer Shakira met with Phoenix Mayor Phil Gordon to lend her celebrity to the campaign opposing the law.