(CBS News) Starting Wednesday, if you're stopped by police in Arizona, you may be asked to show proof that you're in the country legally.
It is the most controversial provision of the state's immigration law, and barely survived a Supreme Court challenge.
Daniela Cruz was brought to America from Mexico as a child. The undocumented immigrant drives without a license. Arizona's new law means she could face more than a ticket if stopped by police.
"Sometimes when there's a police car behind me, I start to get nervous. I start to get shaky, just because I know I can get pulled over for anything," Cruz said.
Police here are required to determine the immigration status of a person stopped or arrested if there's a "reasonable suspicion" they are in the U.S. illegally.
Phoenix Police Chief Daniel Garcia says no one will be stopped without cause.
"That's a point people have a tendency to forget. Before you have reasonable suspicion that someone is here illegally, you have to have reasonable suspicion as a police officer that a crime has occurred, before you have reasonable suspicion on the documentation," said Chief Garcia, adding that a crime could be considered something as small as not stopping at a stop sign.
Chief Garcia said suspects will be held while officers check with federal officials at immigration and customs enforcement.
"The question is how long are we going to detain them. I believe it should be no longer than any other traffic stop -- 10 minutes at the most. If ICE (Immigration and Customs Enforcement) answers, then we have an answer. If they don't answer, then we have an obligation to let that citizen go," Garcia said.
Alesandra Soler of the American Civil Liberties Union says civil right advocates will be watching for signs of racial profiling.
"Law enforcement is saying: 'Trust us, we know better. We're not going to engage in racial profiling.' But the reality is they're ignoring a very real problem of racial profiling that we've had in this state for a very, very long time," Soler said.
Federal authorities say they will answer calls by Arizona authorities to check immigration status, but they will only take custody of illegal immigrants if they are violent criminals or those who have repeatedly crossed the border.