Jack Kurtz / ZUMA PRESS A handful of protesters waited outside the Sandra Day O'Connor Courthouse in Phoenix Wednesday while lawyers from the American Civil Liberties Union and Mexican American Legal Defense and Education Fund sparred with lawyers from Maricopa County and the State of Arizona over the constitutionality of section 2B of SB 1070, Arizona's tough anti-immigrant law.

Immigration rights advocates were delivered a setback after a federal judge ruled on Wednesday that Arizona can start enforcing the controversial “papers please” provision of its immigration law, which had been upheld by a high profile U.S. Supreme Court decision in June but subsequently blocked by a preliminary injunction filed in district court.

U.S. District Judge Susan Bolton lifted that injunction, clearing the way for Arizona police officials to start questioning the immigration status of people they stop for other violations like speeding and suspect are in the country illegally.

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Critics of the provision had argued that it would lead to systematic racial profiling and civil rights abuses. But Bolton said there is no evidence of that, at least not yet, and that the provision could not be challenged on those grounds before the law actually takes effect.

Arizona Governor Jan Brewer, who signed the law in 2010, applauded judge Bolton’s decision to side with the Supreme Court and said she expects thousands of state and local police to begin enforcing the measure in roughly two weeks.

Immigration advocates, though, vowed to continue litigation against the provision based on civil rights challenges and say that the court will eventually strike down the requirement. “The court just gave out a rain check on future challenges on the constitutionality of this law,” Katherine Vargas of the National Immigration Forum told TIME. “I think no state should consider this a green light to follow Arizona’s footsteps. The court was very clear that it was a yellow light—proceed with caution because of the high risk of discriminatory treatment.”

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In essence, civil rights attorneys have an open door to challenge the Arizona law, but they need victims of discrimination to make their case. The National Immigration Law Center, one of the organizations that asked Bolton to block the controversial provision, vowed that it’s only a matter of time before such victims will enable them to return to court. “We’re disappointed but not discouraged by the decision,” said Linton Joaquin, general counsel at NILC. “We’re going to proceed and we’ll be back in court to deal with it.”

Arizona police received intensive training in 2010 on how to implement the Arizona law—preparation that will keep them from discriminating, according to Gov. Brewer. And although some local police organizations initially criticized the measure, arguing that it will cut time and resources spent on combating violent crime, most police groups have since agreed to enforce it if found to be constitutional.

But critics say local police are not equipped to enforce immigration laws and fear the measure will subject thousands of Arizona residents, legal and undocumented, to discrimination based on skin color and a person’s accent. Opponents of the measure say the potential for trouble is magnified in a state as diverse as Arizona, which has a sizeable population of U.S.-born Hispanics.

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Bolton’s decision mirrors one handed down recently by a federal appeals court in Atlanta. The 11th U.S. Circuit Court of Appeals upheld provisions to immigration laws in Alabama and Georgia in August—both modeled on the Arizona law—that allow police authorities to demand immigration documents from people they detain.

The same court, though, sided with immigration advocates when it blocked a provision in Alabama’s law that required public schools to check students’ immigration status. The court also blocked provisions that criminalized the transportation and harboring of undocumented immigrants and a provision that made it a crime for the undocumented to seek work.

In similar fashion, Judge Bolton Wednesday granted a partial victory to pro-immigration groups when she blocked a section of the Arizona law that made it a crime to transport undocumented immigrants within state borders.

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