Wisconsin Vote Is First Shot in Wider Union War Narayan Mahon for The New York Times At a phone bank in Madison, Wis., ahead of a recall vote. Unions seek to remove the governor. GREEN BAY, Wis. - "Recall Walker" bumper stickers dotted the workers" parking lot at the Georgia Pacific paper mill on Day Street here one recent afternoon, proof of their union's role in the effort to oust Gov. Scott Walker from office early for his legislation limiting public employees" bargaining rights. But among the largest donors to Mr. Walker and his cause are the plant's owners, the billionaire industrialists Charles G. and David H. Koch, the latter of whom has said of the recall election to be held in June, "If the unions win the recall, there will be no stopping union power." The recall vote here has been billed as a critical test of labor muscle versus corporate money. But it is only a warm-up for a confrontation that will play out during the presidential election, which both sides view as the biggest political showdown in at least 30 years between pro- and anti-union forces - a labor-management fight writ large. The same national groups flooding the streets and the airwaves in Wisconsin - the Koch-supported group Americans for Prosperity on the right, the A.F.L.-C.I.O., teachers unions and the United Steelworkers on the left - are emerging as important outside supporters of President Obama and Mitt Romney, each side empowered by the Supreme Court's Citizens United decision. That ruling is not only giving wealthy donors like the Kochs greater options for pouring tens of millions of dollars into the presidential election. It is also giving unions - many of them representing workers in some of the major donors" own factories - the ability for the first time ever to spend money from union treasuries for campaigning among nonunion voters. The combination of the squeeze on state budgets, high rates of unemployment and the conservative movement's revived energy provided an opening for Republican efforts, often business-backed, to promote tough-on-labor legislation in key states. Those efforts have succeeded in rolling back gains made by unions over decades, prompting vows from labor to fight back with newly engaged members shaken from self-described complacency. "The steelworkers will be working harder this year than in 2008, because we can see what can happen," Michael Bolton, the director of the United Steelworkers unit representing 48,000 workers in Wisconsin and Michigan - including many hundreds in Koch facilities - said in an interview last week at his office in Menasha, Wis. The steelworkers will be part of a broader effort that national union strategists say will fill the streets in battleground states with hundreds of thousands of their members, who will go door to door telling union colleagues - and, for the first time, nonunion households - why they should vote for Mr. Obama. The A.F.L.-C.I.O."s political director, Mike Podhorzer, said his organization, which reached 25 million voters in 2008, would easily exceed that this year. Officials for the steelworkers say it has been awkward at times to wage partisan battles against the family that owns the factories that employ them. The union's leaders recently agreed on a contract with Georgia Pacific that they considered fair. When liberal groups called for a boycott of Koch products late last year, a Steelworkers vice president, Jon Geenen, said it would harm "the wrong people," writing of a "dilemma and a paradox," namely, "While the Koch brothers are credited with advocating an agenda and groups that are clearly hostile to labor and labor's agenda, the brothers" company in practice and in general has positive and productive collective bargaining relationships with its unions." But, Mr. Bolton said, that has not stopped the union from telling workers at those companies what it believes to be the goal of the Kochs and their allies. "They want ineffective, weak unions," he said, adding, "A lot of these bills didn't directly affect our private sector members, but we realize that we would be the next." In an interview, Mr. Walker called that a "bogus argument," saying he has no plans to pursue right-to-work legislation, as private sector unions have feared. Such legislation lets employees at unionized workplaces opt out of paying union fees. "Private sector unions are my partners," he said. Mr. Walker said that in restricting collective bargaining rights for government workers, save those in public safety, he was confronting a reality facing virtually all state governments with aging, unionized work forces: "We can't sustain our budgets unless we make some reasonable changes." Mr. Walker said charges that he is doing the bidding of wealthy supporters like the Kochs are "the biggest joke out there."