Updated

The American Civil Liberties Union on Tuesday urged a federal appeals court to strike down an Arizona law that denies bail to immigrants in the country illegally, a voter-approved law that Arizona's lawyers call necessary to prevent criminal suspects from fleeing the U.S.

ACLU attorney Cecelia Wang asked a special 11-member panel of the 9th U.S. Circuit Court of Appeals to find the law unconstitutional, saying immigrants are being unfairly singled out as flight risks.

The case marks the latest battle over Arizona's crackdowns on illegal immigration from the past decade. Arizona voters passed the law in 2006 to deny bail to people who are in the country illegally and charged with certain felonies, such as murder, sexual assault and even aggravated identity theft.

Wang argued that no empirical data exist that show immigrants are any more of a flight risk than others cut loose before their final court appearances.

The ACLU and other legal aid groups maintain that the Latino detainees are unfairly held while other nationalities are allowed to put up bond in exchange for their freedom before trial.

"It's unfair to subject a certain subsection of the population to rules that don't apply to everyone else," Wang said.

Lawyers for the state argue that the law prevents defendants from fleeing the country before their court hearings.

Arizona Assistant Attorney General Tim Casey noted that Proposition 100 was approved by 78 percent of the voters. Casey argued that the law is in the "compelling interest in keeping Arizona safe and undocumented workers out of the country."

A smaller three-judge panel rejected the ACLU's arguments in 2011, but the organization appealed to a larger en banc panel of 11 judges.

Four of the judges Tuesday asked questions of both sides but gave no indication of how they would rule. One judge, Marsha Berzon, asked rhetorically, "How does one overturn the will of an overwhelming majority of voters to support the (federal) law?"

It could take months before the court rules, and the outcome can be appealed to the U.S. Supreme Court.

Arizona is one of at least three states with laws confronting the issue of bail for people in the country without authorization. Missouri and Virginia have similar laws.

Arizona passed the no-bail law as it targeted illegal immigration through a series of measures in the Legislature and at the ballot box. It was among four immigration proposals approved by Arizonans in 2006. The no-bail law was proposed by then-state Rep. Russell Pearce, who would later succeed in pushing through Arizona's landmark 2010 immigration enforcement law.

The challengers say the push by the Arizona Legislature to put the measure on the ballot was permeated with the intent to punish people in the country illegally for federal immigration violations. They also argue the state law is trumped by federal law.

The lawyers defending the law say its intent was to improve public safety, not punish people for federal immigration violations. They also said the state law doesn't conflict with federal law.

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