In this AP file photo U.S. District Judge Susan Bolton holds a hearing on immigration. AP file photo/KSAZ-TV FOX 10

PHOENIX - Arizona cannot begin enforcing key parts of last year's immigration law.

In a split decision Monday, the 9th U.S. Circuit Court of Appeals concluded there is sufficient evidence to believe provisions of SB 1070 are an unconstitutional infringement on the exclusive power of the federal government to regulate immigration.

Judge Richard Paez, writing for the 2-1 majority, also said such a conclusion is supported by "the threat of 50 states' layering their own immigration enforcement rules on top of the Immigration and Naturalization Act."

They also said U.S. District Judge Susan Bolton was correct in concluding that letting Arizona enforce the law while its legality is being challenged would cause harm to the interests of the United States. Paez noted that argument was not only advanced by the Obama administration, which is challenging the law, but also by officials from more than a half dozen foreign governments.

That is an important conclusion: Courts must weigh the "balance of hardships" each side would face when enjoining enforcement of a law while its legality is debated.

But the majority's conclusion drew derision from Judge Carlos Bea. While agreeing much of the Arizona law probably is unconstitutional, he said there is no reason states cannot, in some circumstances, help enforce federal laws.

Bea rejected the concerns of Mexico and other countries.

"A foreign nation may not cause a state law to be pre-empted simply by complaining about the law's effects on foreign relations generally," he wrote. "We do not grant other nations' foreign ministries a 'heckler's veto.' "

Senate President Russell Pearce, R-Mesa, who wrote the legislation, promised an appeal to the U.S. Supreme Court.

"There has never been a preemption against states enforcing these laws," he said, adding that the decision is not a surprise.

"We expected - almost could predict - such a thing for the liberal makeup of the 9th Circuit, the most overturned court in the nation," he said. Pearce, who was not permitted to play a role in the defense of the law, also suggested the result might have been different if he had been involved.

Instead, the defense was left pretty much to Gov. Jan Brewer and a team of private attorneys she hired.

"I don't want to criticize their team," Pearce said. "But there are certainly things, being the author of this and being engaged in this battle for over 25 years ... arguments I thought should have been made."

That won't occur again. Bolton earlier this month gave Pearce permission to be part of the defense in the future.

Brewer, in a prepared statement, said she remains "steadfast in my belief that Arizona and other states have a sovereign right and obligation to protect their citizens and enforce immigration law in accordance with federal statute."

Monday's ruling bars enforcement of several sections of the law, including:

• Requiring a police officer to make a reasonable attempt to check the immigration status of those they have stopped.

• Forbidding police from releasing anyone they have arrested until that person's immigration status is determined.

• Making it a violation of Arizona law for a noncitizen to fail to carry federally issued documentation.

• Allowing police to make warrantless arrests if there is a belief people have committed offenses that allow them to be removed from the United States.

• Creating a new state crime for trying to secure work while not a legal resident, which Paez noted Congress chose not to make a crime.

Paez said there is a role for states in enforcing federal immigration law, but it is less broad than SB 1070 allows. He cited laws that allow states to enter into agreement with federal agencies, which include a requirement that the attorney general approve each state officer who is permitted to enforce the law and which functions each person is permitted to enforce.

Paez rejected the state's argument that it has independent authority to enforce and punish violations of federal immigration-registration rules.

Bea, in his partial dissent, said he saw nothing wrong with the part of the law requiring law enforcement officers to question people about their immigration status. Monday's ruling does not resolve the challenge to SB 1070 brought by the Obama administration and others. It deals only with whether the law can be enforced while the case makes its way through the legal system.