The sheriff of Arizona's most populous county is making room in a vast outdoor jail and determined to round up illegal immigrants to fill it. Police from the U.S.-Mexico border to the Grand Canyon are getting last-minute training. And protests and marches are planned throughout Phoenix.

Arizona's new immigration law takes effect Thursday, creating a potentially volatile mix of police, illegal immigrants and thousands of activists, many planning to show up without identification as a show of solidarity.

At least one group plans to block access to federal offices, daring officers to ask them their immigration status.

"Our message for that day is: 'Don't comply, don't buy,'" said activist Liz Hourican, whose group, CodePink, plans to block the driveway for immigration offices in downtown Phoenix.

As both sides prepare, a federal judge is deciding whether to step in and block the law. It requires officers enforcing other laws to check a person's immigration status if they suspect the person is in the country illegally. It also bans illegal immigrants from soliciting work in a public place.

Police across the state scrambled on Tuesday to train officers, including on how to avoid racial profiling, and plan for a potential influx of detainees.

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