In a campaign that is shaping up as a key test of the labor movement and a bellwether for 2012, Ohio voters will decide today whether to throw out a months-old state law that curtails collective bargaining rights for public-sector workers.

Polls show that voters are leaning in favor of rejecting the law, which GOP Gov. John Kasich ushered through the Republican-controlled Legislature in March and which shows up on the ballot as “Issue 2.” The law’s defeat would “be a huge symbolic victory” for labor organizers, said Daniel DiSalvo, assistant professor of political science at City College of New York.

Union organizers and their allies have poured millions into a grass-roots and advertising campaign to defeat the law, one of several recent GOP-led state initiatives to weaken public-sector collective bargaining power. In the wake of a similar law championed by Wisconsin Gov. Scott Walker (R), labor activists attempted without success to recall enough GOP legislators to restore Democrats to power in the Statehouse.

Opponents of the Ohio law gathered 1.3 million signatures to get it on the ballot, more than four times the 321,000 needed.

The battle over Ohio’s Issue 2 reflects union organizers’ larger bid to declare independence from electoral politics and from Democrats, and embrace a year-round issues agenda focused more heavily on state and local policy debates.

The AFL-CIO, in particular, has signaled plans to focus more broadly on grass-roots organizing. Bolstering that effort will be a new AFL-CIO super PAC that will take advantage of relaxed election laws to raise unrestricted money, the federation announced in August.

“We want the labor movement to be a political force in its own right and not an appendage of a political party,” said Thea Lee, deputy chief of staff to the AFL-CIO. Instead of spending the bulk of its money on candidates and party fundraising operations, Lee said, the federation will invest in hiring year-round staff in key states and on building a grass-roots infrastructure.

“You have the possibility for a very different style of political engagement,” she added. “One that is more member-focused and less candidate-focused.”

The shift comes amid mounting political and organizational challenges for the labor movement. Less than 12 percent of American workers belong to a labor union, down from 20.1 percent in 1983, according to the most recent Labor Department statistics. The shift away from an industrial and manufacturing economy and toward global competition has shrunk unions’ ranks and clout.

At the same time, public-sector workers, who represent an ever-larger share of union members, have clashed with state legislators on both sides of the aisle as budget fights put union pensions and benefits on the chopping block. Having failed to win enactment of the Employee Free Choice Act, which would make it easier for workers to certify a union, following President Barack Obama’s election in 2008, labor leaders this year lobbied without success to block free-trade agreements with Colombia, Panama and South Korea. However, they did win assistance for workers displaced by trade deals.

Changing election laws have also altered the political balance of power, giving corporations and GOP-friendly activist groups new access to unregulated money in the wake of last year’s Citizens United v. Federal Election Commission ruling. Pro-GOP outside groups such as American Crossroads spent heavily in the 2010 election, helping put Republicans back in power in the House. In 2012, American Crossroads and its nonprofit affiliate plan to spend $240 million; the group’s organizers argue that they are leveling a playing field that’s been tilted toward unions.

“There’s no question the 2010 election was devastating and disappointing for” the AFL-CIO, Lee said. Labor unions objected to the Citizens United ruling, she said, but added: “We have to play with the rules that are in front of us now. And that means we will be taking advantage of the broader playground that is now available.”

In Ohio, the AFL-CIO has joined other leading unions, including the American Federation of Teachers and the American Federation of State, County and Municipal Employees, in fighting to overturn the collective bargaining law. Business organizers have mounted a counter-effort, around the slogan “Building a Better Ohio,” with local chambers of commerce and other business groups. Total spending by both sides is expected to top $20 million, the New York Times predicted.

A labor win in Ohio could discourage other GOP governors from wading into collective bargaining fights, DiSalvo said. Even if labor organizers lose on Issue 2, the Ohio initiative has suited them up for battle in a state regarded as pivotal to the 2012 presidential contest, he noted. “They have had to create a real grass-roots, on-the-ground network that I’m sure labor and the Democrats will hope that they can sustain over the next 12 months as a campaign or electoral vehicle,” DiSalvo added.