Senate Democrats are pushing new legislation aimed at nullifying Arizona's controversial immigration law -- just in case the Supreme Court, which hears the case Wednesday, upholds the policy.

The proposal, announced Tuesday by Sen. Chuck Schumer, D-N.Y., would stand virtually no chance of passing in the Republican-controlled House. But it marks the latest preemptive challenge by Democrats to a high-stakes Supreme Court decision.

The immigration case arrives at the high court Wednesday just weeks after the justices heard arguments in the multi-state challenge to the federal health care overhaul. Though the justices are not expected to rule in that case until summer, President Obama had cautioned the "unelected" judges against overturning his landmark domestic policy accomplishment -- claiming such a move would be "unprecedented."

Schumer's fallback option on the Arizona immigration case holds a similar message. If the high court upholds the law, the congressional proposal would be a direct rebuke to that decision.

"Immigration has not and never has been an area where states are able to exercise independent authority," Schumer said Tuesday at a Capitol Hill hearing, where he announced he would introduce the proposal should the Supreme Court "ignore" the "plain and unambiguous statements of congressional intent" and uphold the Arizona law.

He said the proposal would only allow states to arrest illegal immigrants if they are operating under an "explicit agreement" with Washington and are being supervised by federal officials. Plus he said the proposal would preempt state governments from enacting their own employment verification laws.

"States like Arizona and Alabama will no longer be able to get away with saying they're simply helping the federal government ... to enforce the law when they are really writing their own laws and knowingly deploying untrained officers with the mission of arresting anyone and everyone who might fit the preconceived profile of an illegal immigrant."

Sen. Jon Kyl, R-Ariz., objected to the hearing Tuesday and suggested Democrats were trying to influence the court.

"I will not participate in today's hearing because it is strictly political theater. The timing of the hearing just one day ahead of the Supreme Court's review of the law suggests that its purpose is either to influence the court's decision or to garner publicity," he said in a statement. "The Supreme Court will decide the case on its merits and that is how it should be."

The Supreme Court case on Wednesday will have national implications, though Arizona is the only state directly involved. Several other states, including Georgia and Alabama, have followed Arizona's lead in implementing their own individually tailored immigration laws.

The Obama administration challenged Arizona on the grounds that its immigration law was a flagrant state overreach.

"Congress vested the Executive Branch with the authority and the discretion to make sensitive judgments with respect to aliens," Solicitor General Don Verrilli argued in the government's brief.

"The decision to admit, detain or remove a particular alien depends not only on resource constraints, but on numerous other considerations that call for a decisionmaker to exercise sound judgment on behalf of the nation as a whole, according to a single standard."

Verrilli argued that Arizona tried to "interpose its own judgments on those sensitive standards."

"For each state, and each locality, to set its own immigration policy in that fashion would wholly subvert Congress' goal: a single, national approach."

But Arizona argued that the current system is broken, and that the state is paying an unfair price for that failure.

"Arizona shoulders a disproportionate burden of the national problem of illegal immigration," attorney Paul Clement argued in his brief. He argued that enforcement attention in California and Texas has turned the Arizona border into a funnel for illegal immigrants, with a third of illegal border crossings occurring there.

"This flood of unlawful cross-border traffic and the accompanying influx of illegal drugs, dangerous criminals and highly vulnerable persons have resulted in massive problems for Arizona's citizens and government," Clement said.

The attorney described Arizona's law as a response to an "emergency situation" -- with illegal immigrants soaking up millions of state dollars in health care and education, posing safety risks to ranchers and cutting into the state's job market.

Two of the key statutes, which have been blocked and will be at issue in Wednesday's arguments, are provisions to bar illegal immigrations from seeking a job and to require law enforcement to check the immigration status of anyone they suspect of being in the country illegally in the course of a routine stop.

A ruling from the Supreme Court is likely to come this summer, in the thick of the presidential election year -- it could either bolster what has been a bold move from the Obama administration's Justice Department to intervene in state issues ranging from immigration to voter ID laws, or stop the administration in its tracks and open the floodgates to even more state laws that challenge federal authority.