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President Obama on Monday slammed Michigan Republicans for their rapid push to pass "right-to-work" legislation, joining other Democrats who were making a last-ditch play to oppose the bill in the final hours before its likely passage.

The president weighed in on the debate for the first time during a stop at an engine plant outside Detroit. He departed from his usual discussion of fiscal crisis negotiations to chide local Republicans for pursuing legislation that would prohibit unions from demanding dues from workers.

"I've just got to say this -- what we shouldn't be doing is trying to take away your rights to bargain for better wages," Obama said, to raucous applause. "These so-called 'right-to-work' laws, they don't have anything to do with economics. They have everything to do with politics.

"What they're really talking about is they're giving you the right to work for less money," he said.

The comments were part of a last-minute attempt by Democrats to pressure Republicans in Lansing. Michigan Democratic Sen. Carl Levin and House Democrats also met Monday with Republican Gov. Rick Snyder and said they urged him to veto the bills. Meanwhile, Michigan House leaders called for more debate before the GOP-led Legislature takes final action on the measures as early as Tuesday.

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Snyder, though, has committed to signing the bill. The Republican-led state House and Senate approved bills last week.

Lansing authorities are bracing for an onslaught of protesters Tuesday. They have increased police presence and plan road closings and parking restrictions around the Capitol.

Senate Democratic Leader Harry Reid also added his voice to the clamor on Monday, calling the push a "blatant attempt by Michigan Republicans to assault the collective bargaining process and undermine the standard of living it has helped foster."

Snyder, though, has said he's "not picking a fight."

"I feel this is solving an issue for Michigan workers. We have hardworking people in Michigan and this is about giving workers choice," the governor said last week.

The surprise move by Michigan Republicans last Thursday to approve the anti-union bills touched off a firestorm in the home of the U.S. auto industry. Following high-profile fights over union privileges in Wisconsin and Indiana, Michigan in an instant became the latest battleground in that struggle.

If the bill passes, Michigan would become the 24th "right-to-work" state in the nation -- and American unions would suffer a stinging defeat in the cradle of the labor movement. Union bosses made clear they won't go down without a fight.

"It's an attack on working families, and we're gonna be there. We're not gonna stand for it," Bernie Ricke, president of the United Auto Workers Local 600, said, according to MyFoxDetroit.

According to MyFoxDetroit, members of Local 600 in Dearborn met Saturday to plan for the massive Tuesday demonstration, even going through a practice protest run with some members pretending to be Tea Partiers in support of "right-to-work" legislation.

Though Republicans control the capital and have the votes to send the bill to Snyder's desk, opponents are planning to mount a legal challenge should that happen. Given the rapid manner with which the bills moved and the fact some demonstrators were kept out of the chambers, Democrats say they'll challenge under open-meetings laws.

The Detroit Free Press also reports that Democrats could try and challenge a provision that exempts police and firefighters.
However, any attempt to bring the proposal to referendum is complicated by the fact that the bill contained an appropriation -- and under Michigan law, appropriations bills cannot be challenged by popular vote.

In order to bring the "right-to-work" bill to referendum, supporters would have to first prove the appropriation to be somehow invalid or inappropriate.

Opponents could also launch recall campaigns against targeted Republicans in retaliation, as they did in Wisconsin following a vote that cracked down on collective bargaining.

Fox News' Mike Tobin and The Associated Press contributed to this report.