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Should it be against the law to give rides to, house or otherwise "harbor" people in the country illegally?

That's the question before a three-judge panel of the 9th U.S. Circuit of Appeals, which heard arguments Tuesday about a controversial section of Arizona's 2010 immigration law that penalizes people for "harboring."

The federal government argued that the section of the law should be blocked. The harboring law was in effect from July 2010 until a lower court last year barred police from enforcing it.

Arizona Gov. Jan Brewer has asked the 9th Circuit to overturn the lower court's ruling.

The issue is whether a statute exclusively applies directly to an alien as opposed to someone who is doing business with or assisting, or is a family member of an alien. This statute is written in the broadest possible terms.

— Mark Stern, a DOJ attorney

Lawyers for Brewer say the law applies only to people violating other criminal laws who also are harboring someone in the U.S. illegally, and it doesn't conflict with federal immigration laws.

The Republican governor's attorneys also say there's no evidence that the ban has been enforced against any people or organizations represented by a coalition of civil rights groups that have challenged the law in court.

The U.S. Justice Department, which has challenged Arizona's immigration law in court but isn't a party in Brewer's harboring ban, successfully petitioned the appeals court to let its lawyers take part in Tuesday's arguments in support of the coalition.

Mark Stern, a DOJ attorney, argued that the federal government was meant to enforce immigration laws, not states, because of its close relationship to foreign policy and other related matters. What's more, the Arizona statute was vaguely written, he said, leading to possible confusion over who would be considered in violation of the law.

"The issue is whether a statute exclusively applies directly to an alien as opposed to someone who is doing business with or assisting, or is a family member of an alien," Stern told the court. "This statute is written in the broadest possible terms."

Brewer's lawyers argue the ban doesn't conflict with federal policies, is aimed at confronting crime and that the law's opponents haven't shown they have legal standing to challenge the prohibition.

"There are many situations where states and the federal government prosecute the same crimes, like some murders and drug crimes," said Kelly Kszywienski, one of the attorneys representing Arizona.

One of the judges, John Noonan, was critical of the way the state's law was worded. He took umbrage with the state, saying the law targeted people who "violate a criminal offense," saying it made the statute "incomprehensible."

"It's nonsense as it stands," said Noonan. "How do you violate an offense?"

The state does not have recent precedent on its side. Another federal appeals court has barred authorities from enforcing similar harboring bans in Alabama and Georgia.

Also, Arizona's harboring law has gotten little, if any, use by police. Two weeks before Bolton shelved the ban, she said during a hearing that she knew of no arrests that were made under the provision.

The prohibition had been overshadowed by other parts of the law, including a requirement that went into effect in September that officers, while enforcing other laws, question the immigration status of those suspected of being in the country illegally.

The U.S. Supreme Court upheld the questioning requirement in July, but also struck down other sections of the law, such as a requirement that immigrants obtain or carry registration papers. The nation's highest court didn't consider the harboring ban.

Last month, the 9th Circuit upheld a decision by Bolton that prohibited police from enforcing a section of the 2010 law that made it illegal for people to block traffic when they seek or offer day labor services on streets.

Omar Jadwatt, the American Civil Liberties Union attorney arguing the case for the coalition challenging the law, said the real concern is not just for people living in the U.S. illegally.

"It's concerning to anybody who regularly gives rides to friends and neighbors, or family members who lack status. It should be alarming to people who own rental accommodations," Jadwatt said. "It's also a concern for 'Dream Act kids,' who have permission from the federal government to be here, but Arizona doesn't think that's good enough."

Based on reporting by the Associated Press.

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