PHOENIX » A judge in Arizona ruled today that police can immediately start enforcing the most contentious section of the state’s immigration law, marking the first time officers can carry out the so-called “show me your papers” provision.

The decision by U.S. District Judge Susan Bolton is the latest milestone in a two-year legal battle over the requirement. It culminated in a U.S. Supreme Court decision in June that upheld the provision on the grounds that it doesn’t conflict with federal law.

Opponents responded to the Supreme Court decision by asking Bolton to block the requirement on different grounds, arguing that it would lead to systematic racial profiling and unreasonably long detentions of Latinos if it’s enforced. She said early this month she wouldn’t block it, and gave the go-ahead today for the law to take effect.

The section of the law requires that officers, while enforcing other laws, question the immigration status of those suspected of being in the country illegally. The “show me your papers” name comes from opponents.

Arizona’s law was passed in 2010 amid voter frustration with the state’s role as the busiest illegal entry point into the country. Five states — Alabama, Georgia, Indiana, South Carolina and Utah — have adopted variations on Arizona’s law.

A call to the office of Gov. Jan Brewer, who signed the measure into law, wasn’t immediately returned this afternoon.

A coalition of civil rights groups is awaiting a ruling from the 9th Circuit Court of Appeals on their latest effort to prevent the questioning requirement from taking effect.

“Our next step is seeing what happens with that,” said Linton Joaquin, a lawyer for National Immigration Law Center, one of the groups in the coalition.

Some backers of the law questioned the level of cooperation they will get from federal immigration agents, who will be called to verify people’s immigration status and be responsible for picking up illegal immigrants from local officers.

Federal immigration officers have said they will help, but only if doing so fits with their priorities, including catching repeat violators and identifying and removing those who threaten public safety and national security.

If federal agents decline to pick up illegal immigrants, local officers in some cases will likely have to let them go unless they’re suspected of committing a crime that would require them to be brought to jail.

Bolton is the judge who initially blocked the law after the Obama administration challenged it on the grounds that federalimmigration law trumps state law.

The case made it all the way to the U.S. Supreme Court. There, justices barred police from enforcing other parts of the law, including a requirement that immigrants obtain or carry immigration registration papers. But they allowed the questioning requirement — to supporters the most important part — to move forward.

The latest challenge from a coalition of civil rights, religious and business groups — which Bolton also denied — said Latinos in Arizona would face systematic racial profiling.

But Bolton agreed with the state’s lawyers that the law’s opponents were merely speculating on those claims. She did leave the door open to challenges once the law is in effect, if the claims can be proven.