PHOENIX (AP) — A judge has ruled that police in Arizona can immediately start enforcing the most contentious section of the state's immigration law.

The ruling on Tuesday by U.S. District Judge Susan Bolton marks the first time police can carry out the 2010 law's requirement that officers, while enforcing other laws, question the immigration status of those they suspect are in the country illegally.

The requirement known by the law's critics as the "show me your papers" provision has been at the center of a two-year legal battle that culminated in a U.S. Supreme Court decision that upheld the requirement.