Justices will hear arguments by a coalition of civil rights and business groups who contend the 2007 law infringes on the exclusive right of the federal government to regulate immigration.

A federal judge in Phoenix did not see it that way. And his ruling was upheld more than a year ago by the 9th Circuit Court of Appeals.

But what's different now is that the Obama administration has added its voice to the debate. Acting Solicitor General Neal Katyal, in legal papers filed with the high court, argued the Arizona law specifically runs afoul of a federal law that bars states from imposing any sort of penalties on those who employ people not in the country legally.

Hanging in the balance is what is formally known as the Legal Arizona Worker Act. It was approved by the Republican Legislature and signed by Democratic Gov. Janet Napolitano over the objections of business interests.

In fact, Napolitano, now the Homeland Security secretary in the Obama administration that is trying to kill the law, said at the time she approved it "because it is now abundantly clear that Congress finds itself incapable of coping with the comprehensive immigration reforms our country needs."

Napolitano, through an aide, declined to comment on the current fight.

But a ruling striking down the law could have even broader effects: If the justices conclude that federal immigration laws totally preempt any state rules, that likely would be the death knell for SB1070, the controversial Arizona law approved earlier this year to give police more power to detain and arrest suspected illegal immigrants.

The law is billed by supporters as Arizona's attempt to dry up the supply of jobs as a way of deterring illegal immigration.

But the Immigration Reform and Control Act, approved by Congress in 1986, precludes states and cities from imposing any civil or criminal penalties on companies for hiring illegal immigrants. The same law, however, allows states to have their own "licensing or similar laws."

Sen. Russell Pearce, R-Mesa, said he crafted the law to fit that exception by making the suspension or revocation of a state license the sole penalty for hiring undocumented workers. The rulings of the trial and appellate courts would appear to back his contention.

But attorney Julie Pace, who is representing the Arizona Chamber of Commerce and Industry, said the judges got it only half right.

She conceded that states can take away business licenses.

Pace argued, though, that can happen only after a firm is found guilty by a federal court or similar federal process of knowingly hiring illegal immigrants. She said state judges lack legal authority to make that decision.

Katyal, in his own arguments to the Supreme Court, agreed that the procedures under the Arizona law to determine guilt or innocence of a business owner run afoul of federal regulations.

He said there are procedures that cover cases where federal officials accuse employers of hiring undocumented workers, including the ability to appeal. That, he said, is not the case in Arizona.

"Proceedings (under the Arizona law) occur before local judges, with no possibility of federal district court review," Katyal said. And he said Arizona law, unlike its federal counterpart, has no provision banning discrimination.

Pearce, who will be attending the court hearing, disagreed.

He said the law has safeguards for companies, starting with the requirement that prosecutors prove that an employer knowingly broke the law in order to obtain a conviction. He said that protects them against prosecution for innocent mistakes.

And Pearce said the law also gives a "rebuttable presumption" of innocence to any firm that used the federal government's online E-Verify system to check whether new employees are legally entitled to work in this country.

Gov. Jan Brewer, who also will be in Washington for the hearing, said that, for her, the issue is simpler.

"I think we have a responsibility given that our borders aren't secure," she said. The governor said the state needs "to do whatever is necessary" to curb illegal immigration.

Brewer said the question of preemption would be an issue only if the federal government were doing its job.

"In lieu of that, Arizona's stepping up and trying to do the best job that we can given the tools that we are enabled with by the decision of the Legislature," she said.

A separate part of the legal challenge deals with that E-Verify program itself.

The law specifically requires companies to use the federal database with all new workers. Lower courts rejected arguments by foes of the legislation that such a mandate is illegal.

The newest Supreme Court justice, Elena Kagan, will not participate in this hearing because the Department of Justice filed its objections to the Arizona law while she was still solicitor general.

A ruling is not likely until spring.