A federal judge ruled Wednesday that Arizona authorities can enforce the most contentious section of the state's immigration law, which critics have dubbed the "show me your papers" provision.

The ruling by U.S. District Judge Susan Bolton clears the way for police to carry out the requirement that officers, while enforcing other laws, question the immigration status of those they suspect are in the country illegally.

The provision has been at the center of a two-year legal battle that resulted in a U.S. Supreme Court decision in June upholding the requirement, ruling against the Obama administration, which filed the initial challenge.

The Obama administration declared a measure of victory at the time, as the court said local police cannot detain anyone on an immigration violation unless federal immigration officials say so.

After the nation's highest court weighed in, opponents asked Bolton to block the provision outright by arguing that it would lead to systematic racial profiling and unreasonably long detentions of Latinos if it's enforced.

Lawyers for Arizona Gov. Jan Brewer, however, urged the judge to let the requirement go into effect, saying the law's opponents were merely speculating in their racial profiling claims. The Republican governor's office also said police have received training to avoid discriminatory practices and that officers must have reasonable suspicion that a person is in the country illegally to trigger the requirement.

In her ruling, Bolton said the court will not ignore the clear direction from the Supreme Court that the provision "cannot be challenged further on its face before the law takes effect." She reiterated the high court's interpretation that the law might be able to be challenged as unconstitutional on other grounds.

The Obama administration's case was based on the argument that federal immigration law trumped Arizona law. The challenge didn't confront racial profiling.

Arizona's law, known as SB1070, was passed in 2010 amid voter frustration with the state's role as the busiest illegal entry point into the country. Five other states -- Alabama, Georgia, Indiana, South Carolina and Utah -- have adopted variations.

To the supporters, the questioning requirement was the most important part of Arizona's law, which aimed to reduce the problems associated with illegal immigration through enforcement of the state's policy.

Immigrant rights groups say the requirement presents the most opportunities for civil rights abuses.

Shortly before the law was to take effect in July 2010, Bolton prevented police from enforcing the questioning requirement and other parts of the statute, ruling the Obama administration would likely succeed in its challenge.

Brewer, who signed the measure, appealed the ruling, lost at the 9th Circuit Court of Appeals and took her case to the Supreme Court.

Less controversial sections of the law have been in effect since late July 2010, but have rarely been used.

Brewer's office said the law is expected to go into effect shortly.

"Certainly Gov. Brewer is pleased with this decision," said governor's spokesman Matthew Benson. "She believes it's time SB1070 is implemented and so that we can see how effective this law is in practice."

Karen Tumlin, an attorney for the National Immigration Law Center, said her office was "considering our legal options" after Bolton's ruling.

"We were surprised and disappointed," said Dan Pochoda, legal director for the American Civil Liberties Union of Arizona.

The chief sponsor of SB1070, former state Senate President Russell Pearce, didn't immediately return a call for comment Wednesday afternoon and neither did the office of Maricopa County Sheriff Joe Arpaio.

Lyle Mann, executive director of the Arizona Peace Officer Standards and Training Board, said law enforcement statewide has been trained on how to implement SB1070 and had been awaiting a start date.

What's unclear, he said, is how the federal government will respond to requests for immigration checks and what the relationship will be between the U.S. Immigration and Customs Enforcement and Arizona police.

"We don't know, and I don't know if anybody knows until that starts to happen," Mann said.

Amber Cargile, the ICE spokeswoman in Arizona, declined comment and directed inquiries to the national office.

Bolton did, however, grant a preliminary injunction against a statute making it illegal to harbor individuals suspected of being in the country illegally.