With unprecedented amounts of cash set to flood the airwaves this year, campaign finance reform advocates have slowly began to coalesce around a far-fetched idea: How about a constitutional amendment to ban big money in politics?

The idea, floated by various left-leaning groups, is to build a grassroots campaign behind an amendment to reverse Citizens United, which laid the groundwork for the Super PACs that are expected to pump unlimited sums into the 2012 campaign, with untold consequences for our politics.

Now that campaign is about to take a new turn: Lefty groups are going to call on President Obama himself to support such a step.

MoveOn is set to go out to its list with an email calling on members sign a petition pressuring Obama as follows:

Hundreds of millions of dollars are being spent to influence elections and we have no clue which corporations are behind it.

There are two big things President Obama could do right now that would start to turn the tide: 1) He could sign an executive order to require corporations that do business with the government to disclose their political spending right away for this election, and 2) he could declare his strong support for a constitutional amendment to get big money out of politics permanently.

Public Campaign Action Fund, which is also calling on Obama to support this course, just released some new polling from the Dem firm Democracy Corps that shows strong public opposition to Citizens United. It shows that 62 percent oppose Citizens United and more than half support a consitutional amendment to undo it.

More importantly, it shows that concern over secret money in politics is directly linked to concern about the excessive influence of big banks, corporate lobbyists and the wealthy over our politics — which have been pushed to the forefront of the conversation by various factors.

If the big labor unions — which have loudly condemned Citizens United — join this campaign to pressure Obama to call for such a step, it could get interesting. After all, organizers point out, after the decision Obama vowed a “forceful response.”

It seems unlikely that Obama would make such a move in an election year. But lefty groups will argue that it could make good politics, dovetailing neatly with the Dem strategy of painting Mitt Romney — who supports doing away with all limits on campaign contributions — as the walking embodiment of everything that’s wrong with our current system and of all the ways it is rigged on behalf of the rich corporations, and against the middle class. And they’ll argue that once voters find themselves swamped by nonstop negative ads for months, the public will be even more receptive to this idea.

At a minimum, this could prove another good frontier for progressive organizing.