But dozens of cities say the policy aids police by making it easier for people to report crimes.
When responding to an incident, Oakland police will gather the usual who, what, when of those involved. But there's one question they won't ask: Are you here in this country legally?
That's because Oakland calls itself a "sanctuary city," one of dozens across the United States that have policies directing local police or officials to stay out of immigration matters.
For Lt. Chris Mufarreh, who patrols the heavily Hispanic Fruitvale neighborhood, "sanctuary" soothes fears among immigrants about coming forward when they are crime victims or witnesses. But for resident Steve Kemp, who is organizing a protest of the policy, the police are shirking their duty to uphold the law.
Sharply divided views on sanctuary policies are emerging on the national stage. A Florida congresswoman introduced a bill this month that would withhold some federal funds to sanctuary cities. Meanwhile, Republican presidential contender Mitt Romney has been criticizing rival Rudolph Giuliani for the former mayor's sanctuary policy in New York City.
With the demise of a comprehensive immigration deal this year, in congress opponents of illegal immigration are pushing for greater enforcement mechanisms, including help from local law-enforcement. But for immigrant advocates and many police departments, that goal draws local resources into an area of federal responsibility and undermines successful community policing efforts.
"If police are seen as immigration enforcers, members of immigrant communities will simply be afraid to talk to them," says David Harris, a law professor at the University of Toledo in Ohio and author of "Good Cops," a book on preventive policing. "When that kind of fear is rampant in the community, the predators know this right away."
He cites Austin, Texas, which faced a scourge of violence, particularly against immigrants carrying large amounts of cash. The fix: Offer identification cards for immigrants to open bank accounts and get the word out that police weren't interested in immigration status. Reports from witnesses spiked, followed by a drop in the violence, says Mr. Harris.