Arizona, which borders Mexico, has an estimated 500,000 illegal immigrants, according to the US Department of Homeland Security.
The issue is huge in Arizona as more people cross illegally into the US through that state than anywhere else, amounting to nearly half those caught in the past fiscal year, according to US Customs and Border Protection.
So it made nationwide news late Monday when lawmakers in the Arizona Senate voted to approve the bill, which would make it a state crime to be in the country illegally and require local police to enforce federal immigration laws.
The bill is regarded as the toughest measure yet taken by any US state to curb illegal immigration. Gov. Jan Brewer, a Republican, has five days to veto the bill or sign it into law.
If Brewer signs it, Arizona would be the first state to criminalize illegal immigration. Arizona has become the flash point in the immigration debate where tens of thousands illegal immigrants have led to state and local restrictions including a recent law that requires government workers to report illegal immigrants seeking public benefits.
Arizona has adopted several measures to combat illegal immigration, including a 2007 law requiring employers to use a federal database to verify the legal status of employees-a measure that is optional in other states. Under federal law, a business can lose its license and can face hefty fines for knowingly hiring illegal immigrants, but businesses are not required by federal law to verify if information or documents provided by employees - such as social security numbers and photo identification - are fake or stolen.
Arizona's law also 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.
States generally do not compel police or other officials, like hospital staff, educators or workers of local motor vehicle departments, to investigate legal status over concerns it would force illegal migrants to avoid schools and hospitals, or would dissuade them from cooperating with police investigations.
Many throughout the US are critical of Arizona's tough legislation:
"The Arizona Legislature has just stepped off the deep end of the immigration debate, passing a harsh and mean-spirited bill that would do little to stop illegal immigration. What it would do is lead to more racial profiling, hobble local law enforcement, and open government agencies to frivolous, politically driven lawsuits," said The New York Times in an editorial Tuesday.
The founder of the border-watch group the Minuteman Civil Defense Corps, Chris Simcox, believes that inadequate border enforcement and federal inaction have forced Arizonans to act.
"Arizona is 'Ground Zero' not only for illegal immigration, but for exercising our rights - for fighting back," says Simcox, who is challenging Arizona Sen. John McCain in the Republican primary later this year.
Immigration is a bitterly fought issue throughout the United States where between 12 and 20 million illegal immigrants live and work in the shadows.
Republican state Sen. Russell Pearce, the author of many of those policies, says lawmakers have a responsibility.
"Either you enforce the law or you become a victim to your laws," he has said.
