How else would this policy be executed?

"The law requires state and local police to determine the status of people if there is "reasonable suspicion" that they are illegal immigrants and to arrest people who are unable to provide documentation proving they are in the country legally.
[...]
Opponents of the Arizona law, some of whom held a vigil outside Brewer's home on Monday to urge her to veto the measure, say it is unconstitutional and would discriminate against Latinos.
"You cannot tell if a person walking on a sidewalk is undocumented or not ... (so) this is a mandate for racial profiling," said Pablo Alvarado, director of the National Day Laborer Organizing Network.

Reuters: Arizona passes tough illegal immigration law, April 19, 2010

“I sure hope it does have an effect,” Mr. White said of the new law as he packed his car with groceries. “I wouldn’t want to show proof of citizenship, but I also don’t feel it is racial profiling. You are going to look different if you are an alien, and cops know.” 

NY Times: Growing Split in Arizona Over Immigration, April 25, 2010

"Hispanics and Latinos (of any race) [make] up 29.0% of Arizona's population."
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