By ADAM NAGOURNEY
Published: October 1, 2012

LOS ANGELES — The battle to curb labor’s political clout has moved from Wisconsin to California, where wealthy conservatives are championing a ballot measure that would bar unions from donating to candidates. Labor leaders describe it as the starkest threat they have faced in a year of nationwide challenges to diminish their once-formidable power.

The measure, Proposition 32 on the November ballot, would prohibit both unions and corporations from making contributions, but the corporate provision is far less stringent than the one aimed at unions, analysts said. If passed, it would also bar unions from using automatic payroll deductions to raise money for political campaigns, a major source of labor’s political funding.

“This would be a big deal for unions if it passes since it would largely cut off their participation in state and local California politics,” said Daniel J. B. Mitchell, a professor emeritus at the U.C.L.A. Anderson School of Management.

The prospect that Proposition 32 could become law in an overwhelmingly Democratic state that has a rich history of union activism has alarmed labor leaders. A victory here, they argued, would pave the way for similar efforts across the nation.

“This is intended not to hobble us, this is intended to eviscerate us,” said Art Pulaski, the head of the California Labor Federation. “If they can do it in California, they can do it everywhere and anywhere.”

Supporters of the proposition described it as an evenhanded attempt to curb special interests, pointing to language addressing both unions and corporate donations. The payroll deduction applies to unions as well as corporations, though sponsors of Proposition 32 said the corporate use of payroll deductions in California was rare.

“We wanted to do something that hit hard at the unions and the corporations that are responsible for creating deep discord in California,” said Michael D. Capaldi, a former chairman of the Lincoln Club of Orange County, a conservative organization, who helped write the initiative. “So we drafted an initiative that deals with both unions and corporations. We don’t say it affects them both equally, but it does affect both significantly.”

Unions have raised more than $37 million to defeat the proposition, with most of the money coming from the California Teachers Association. Proposition 32, which was drafted by the Lincoln Club, whose members have included Richard M. Nixon and John Wayne, has raised about $9 million. Most of the proposition’s financial support comes from the America Future Fund, an organization with ties to the donor network spearheaded by Charles and David Koch, the billionaire industrialists who have contributed heavily to defeating President Obama and were big backers of Scott Walker, the Republican governor of Wisconsin who championed measures to severely curb the power of public employee unions there.

The second major backer is Charles T. Munger Jr., a wealthy physicist who was the largest contributor to a 2010 initiative creating a nonpartisan commission to draw Congressional and legislative district lines.

Opponents say that if Proposition 32 wins, they would almost certainly challenge it in court.

Polls show the contest as tight, with opponents having an edge. In a U.S.C. Dornsife/Los Angeles Times poll released last week, 44 percent of respondents said they would oppose Proposition 32, compared with 36 percent who said they supported it. But 19 percent said they remained undecided.

By design or not — and some union officials said they believed it was by design — the fight has forced unions to divert money from what had been their top priority: winning approval of an initiative by Gov. Jerry Brown to pass temporary tax increases to head off nearly $6 billion in new cuts in state spending.

“Labor has to stop everything it is doing to defend against this,” said Peter Dreier, the director of the Urban and Environmental Policy Department at Occidental College. “It’s pretty effective in forcing the unions to spend a lot of their resources to stop this from passing.”

Proposition 32 has drawn opposition from the League of Women Voters and major editorial boards, because of its unequal treatment of labor and corporations. The ban on contributions would not apply, for example, to limited corporations and real estate trusts, two major sources of business contributions here.

To read entire story, click here.