A federal judge is allowing the most controversial piece of Arizona's tough immigration law to proceed, ushering in a new era of immigration enforcement in the state.

The Arizona law has been intensely polarizing in large part because of a provision that requires law enforcement officers to check the immigration status of people whom they suspect to be in the country illegally. Critics labeled that provision a "papers please" measure that would lead to racial profiling.

U.S. District Judge Sharon Bolton lifted a two-year suspension of the measure on Wednesday, reacting to a recent Supreme Court decision that left the police checks measure intact while invalidating other parts of the law.

The Obama administration had sued Arizona, arguing that the law unconstitutionally sought to give local law enforcement agents the power to enforce immigration laws -- an authority, the Department of Justice said, that falls solely to the federal government. The Supreme Court sided with the administration on several pieces of the law, including those that made it a state crime for undocumented immigrants to work or not carry documentation, but preserved the police checks.

Judge Bolton invalidated a separate provision that would have banned harboring or transporting undocumented immigrants. That measure has drawn heavy criticism from religious groups who have argued that it would prohibit some of their basic philanthropic activities.

"Federal immigration law creates a comprehensive system to regulate the transportation, concealment, movement, or harboring of unlawfully present people in the United States. In crafting federal regulation of these activities, Congress permitted state law enforcement officials to arrest for violations of federal law, but did not allow for state regulation in the field," Bolton wrote.

Even though the Supreme Court has already ruled on the law, more litigation could be on the horizon. In handing down the decision, Chief Justice John Roberts wrote that there was still a "basic uncertainty about what the law means and how it will be enforced," and added that the ruling "does not foreclose other preemption and constitutional challenges to the law."

The Obama administration made its case purely in terms of the doctrine of "pre-emption," saying Arizona was claiming enforcement powers that rightfully belonged to the federal government.

The Justice Department did not make a civil rights-based argument -- for instance, it did not charge Arizona with violating the Equal Protection clause of the Fourteenth Amendment, which guarantees uniform treatment under the law. Immigration and civil rights activists will be closely watching how the Arizona law is implemented to see if there is a case to be made.