PHOENIX — A federal appeals court on Tuesday ruled Arizona cannot enforce yet another provision of its controversial 2010 law aimed at illegal immigration.

The three-judge panel of the 9th U.S. Circuit Court of Appeals said the law designed to punish those who knowingly transport or harbor someone in this country illegally is so badly written as to be “unintelligible.” But Judge Richard Paez said that’s only part of the problem with that part of SB 1070.

He said Congress already has approved a series of laws aimed at those who aid people here illegally, which makes it off-limits for states to create their own laws — and set up their own systems for prosecuting violators.

Paez warned that letting Arizona enforce its own immigration laws would let the state undermine federal policies like Deferred Action for Childhood Arrivals, or DACA.

Tuesday’s ruling is not the final word on the measure, but affirms a lower-court ruling barring the state from enforcing it while it is litigated.

In upholding that ruling, the judges concluded the challengers are likely to succeed in convincing them the statute is illegal.

Attorney General Tom Horne, vowed to appeal. He said Arizona enacted SB 1070 because federal officials were not enforcing federal immigration laws.

And Gov. Jan Brewer, who signed SB 1070 into law, criticized the conclusion the state can’t make up and enforce its own laws.

“I think that we have that right,” the governor said. “But what befuddles me is what do they expect our law enforcement officers to do? They’re breaking the law.”

But attorney Karen Tumlin of the National Immigration Law Center, said there is a role for state and local police is to work within federal laws.

“Congress is really clear,” she said.

“They said, ‘Hey, state and local officials, you can make arrests for our federal provision. But then, we got it from there. We’re in charge of deciding whether or not this fits our priority. We’re in charge of deciding whether it violates federal law. We decide when we prosecute and when we don’t.’ ”

Paez said Congress clearly wanted only federal prosecutors to decide how to handle immigration law violations.

“By allowing state prosecution of the same activities in state court, Arizona has conferred upon its prosecutors the ability to prosecute those who transport or harbor unauthorized aliens in a manner unaligned with federal immigration enforcement policies,” the judge wrote.

He said that would allow Arizona to effectively charge people with violating a federal law, “even in circumstances where federal officials in charge of the comprehensive scheme determine that prosecution would frustrate federal policies.”

Paez cited the DACA program which allows certain people here illegally who arrived in this country as children and meet other conditions to remain and work. At the same time, Brewer has deemed those in the program “unlawfully present aliens,” a category she uses to deny them the ability to get a state driver’s license.

Paez said that if Arizona were allowed to enforce this law “it would authorize the prosecution of those who transport or provide shelter to these young people despite the fact that the federal government has chosen to allow them to stay, and work, in the country.”

The issue of how badly written the law is stems from wording that make it illegal for someone who is “in violation of a criminal offense” to knowingly or recklessly transport, conceal, harbor or shield an unauthorized alien.

“One cannot violate an action,” Paez wrote. “One can only violate an object, such as a law or an agreement.” Paez said that makes the law effectively read to be “in violation of a violation of the law, which is, of course, nonsensical.”

Attorneys for the state asked the court to essentially read the language as making sense. But Paez declined, saying it was up to the Legislature, not the court, to rewrite the law.

But even if lawmakers did rewrite the measure, the federal pre-emption issue remains.