The US Supreme Court on Wednesday will take up Arizona's controversial law cracking down on illegal immigrants as it prepares to weigh in on yet another heated issue in the 2012 election.

After three days of hearings on President Barack Obama's landmark health reform law last month, the court will again examine the separation of federal and state powers when it looks at the legality of Arizona's identity checks.

The top US court announced in December that it would review the 2010 law in the southwestern state, which would allow police to stop suspected illegal immigrants and demand proof of citizenship without probable cause.

The law -- portions of which have been suspended after court challenges by the Obama administration -- is among several pieces of state legislation that the White House says infringe on the federal government's authority.

The court is likely to deliver its rulings on both the immigration and the health care cases in June -- just a few months before voters go to the polls to decide whether Obama should be given a second term.

Last year, lower courts opted to strike sections of the law they said would place a burden on legal resident aliens in Arizona, where a third of the 6.6 million people is foreign-born and more than 400,000 are illegal immigrants.

But Arizona appealed, claiming that "the federal government has largely ignored Arizona's pleas for additional resources and help" in stemming the tide of illegal immigration into the state, which borders Mexico.

Arizona governor Jan Brewer -- who earlier this year was caught on camera pointing her finger in Obama's face in what looked to be a testy exchange on an airport tarmac -- has asked the high court to reinstate the suspended sections.

Beyond the identity checks without probable cause, the other sections in question would make it a crime to be in the United States unlawfully and require non-citizens to carry their identity papers with them at all times.

Also at issue is a provision that would make it a crime for illegal migrants to seek work, and one authorizing law enforcement officials to stop anyone they believe may have committed a crime that would result in their expulsion.

Critics have charged that the law would encourage racial profiling, while supporters say tougher rules are needed to curb illegal immigration.

Anthony Romero, director of the American Civil Liberties Union (ACLU), said it would be a "very dark moment" for US jurisprudence if the Supreme Court upholds the law, paving the way for legally-sanctioned discrimination.

"For the first time they would allow law enforcement to use the color of your skin, your race, your ethnicity... It's a law that is very Draconian," he told AFP.

"This case has huge implications for law enforcement and for civil rights. If the Supreme Court decides the wrong way, it's going to be a battle all over the country, state after state," Romero said.

Mexico and 17 other countries have also filed arguments with the Supreme Court opposing the law, saying the delegation of authority over such matters to individual states threatens bilateral relations with Washington.

A new study out this week by the Washington-based Pew Hispanic Center meanwhile found that the net flow of Mexican immigrants to the United States had dropped to zero due to the weakening of the American economy.

Heightened US border enforcement, a rise in deportations, improving economic conditions in Mexico and a falling birth rate there have compounded the trend, it said.

In its motion filed with the Supreme Court, Arizona argues that SB 1070 is "perfectly congruent with federal law and federal objectives."

At least 36 states have introduced legislation with elements similar to those in Arizona, five of which have been passed.

Eight of the court's nine justices will hear the case. Justice Elena Kagan, who once served as Obama's solicitor general, has recused herself. If there is a four-four tie, the lower court's decision to strike the provisions will be upheld.