WASHINGTON (AP) — Unions say they are gearing up to spend more than $400 million to help re-elect President Barack Obama and lift Democrats this election year in a fight for labor's survival.

Under siege in state legislatures around the country — and fearing the consequences of a Republican in the White House — union leaders say they have little choice as they try to beat back GOP efforts to curb collective bargaining rights or limit their ability to collect dues.

"People are digging deeper," said Larry Scanlon, political director of the country's largest public workers union, the American Federation of State, County and Municipal Employees. "If Republicans take over the presidency, Congress and enough state legislatures, unions will be out of business, pure and simple."

Scanlon's union was the biggest overall spender in the 2010 midterm elections, doling out about $93 million to help state and federal candidates, mostly Democrats. This year, AFSCME is expected to spend at least $100 million or more on political action, including television advertising, phone banks and member canvassing. The effort is to help the president, Democrats running for the House and Senate, gubernatorial candidates and key state lawmakers.

With increased spending planned by other labor groups, including the powerful Service Employees International Union and the AFL-CIO, unions are likely to top the $400 million they spent to help elect Obama four years ago.

Not all union expenditures on political action are publicly disclosed, so some numbers are based on self-reporting. But unions have long been known as one of the most reliable supporters of Democratic candidates and their efforts have increased with every election as the threats to organized labor grow.

Unions already spent more than $40 million last year to successfully repeal an Ohio law that restricted collective bargaining rights and to recall lawmakers who backed a similar measure in Wisconsin. They are spending millions more in a bid to recall Republican Wisconsin Gov. Scott Walker, who led the charge to curb public employee union rights as a way to balance the state's budget.

But unions are being spread thin as they deal with a new wave of measures they say are designed to weaken their clout. Indiana passed a right-to-work measure earlier this month, and Republicans in New Hampshire are pushing a similar bill. Legislatures in Arizona and Utah are weighing measures to limit bargaining rights for their public employees.

"Part of the Republican strategy is to try to bleed us," said Mike Podhorzer, political director of the AFL-CIO. "There are certainly more union members now who understand the importance of political engagement and are willing to go door-to-door and make phone calls and do campaigns."

Tim Phillips, president of the conservative anti-tax and anti-regulation group Americans for Prosperity, denied any grand strategy to weaken unions. His group, founded with the support of billionaire brothers Charles and David Koch, spends millions on anti-Obama and anti-union ads across the country.

"It's not accurate to say there's some master plan to drain resources," Phillips said. "These are genuine public policy efforts."

But Phillips said he thinks that, for the first time, unions have to confront organized grassroots opposition in a number of states.

"And Americans for Prosperity is absolutely a key component in that," Phillips said. "The unions have always had the advantage and we are now matching them."

The stakes are even higher for unions this year, as GOP presidential hopefuls seeking conservative support have made unions a regular punching bag. Former Massachusetts Gov. Mitt Romney says he would support states pursuing right-to-work laws and seek to ban unions from using automatic dues deductions for politics. He would also reverse Obama's executive order encouraging the use of union labor in large government construction projects.

AFSCME, the 1.6-million member union, started early this year, spending $1 million on television ads during Florida's GOP presidential primary to weaken Romney, the candidate organized labor presumes will emerge as the Republican nominee.

The SEIU teamed up with Priorities USA Action, the major super PAC backing Obama, to buy ads in Florida and Nevada accusing Romney of flip-flopping on immigration policy. SEIU is the single largest contributor to Priorities USA after making a $500,000 contribution in December.

The 2.1 million-member union is expected to spend at least $85 million to help Obama win, similar to what it spent in 2008, spokeswoman Jennifer Farmer said.

So far, unions are finding a way to pay for all the political spending. Union members are contributing more to political action committees, agreeing to special assessments and spending more time working on political causes.

The AFL-CIO is following a new strategy outlined last summer to contribute less money to specific candidates and spend more on building its infrastructure. The goal is to lay a foundation for year-round mobilization that keeps going in the months following an election. Competing for the union money are the various races, from president to state lawmaker.

"We have to use 2012 not just to win for its own sake, but to use as a springboard for 2014 when the governors in all these states are up," Podhorzer said.

The new strategy emerged after some unions grew frustrated last year that Democrats in Congress were not doing enough to stand up for labor's agenda.

The AFL-CIO also started its own labor super PAC, which allows it to raise unlimited amounts of money and mobilize support beyond its traditional base. The new super PAC has already pulled in $3.7 million.