MADISON, Wisconsin — Republican attempts to disband public workers unions in Wisconsin and other key states are part of a broad strategy to undermine US President Barak Obama and his Democrats at the ballot box, analysts said.

Unions have been the biggest sources of financial and grass roots, get-out-the-vote organizational support for Democrats and have long been a target of business-backed Republicans.

But they've seen their power and membership rolls shrink as the manufacturing sector declined and shifted to anti-union southern states, and now represent just 12 percent of US workers.

Public workers account for more than half of union rolls, even though a dozen states prohibit state and local government workers from forming unions.

And now Republican governors in Wisconsin, Ohio, Indiana and Iowa are looking to curtail or even eliminate collective bargaining rights for state and local government employees.

The move to bust public unions is part of a broader attempt "to bring us closer to a more permanent Republican majority," said Marjorie Hershey, a political science professor at Indiana University.

Republicans won a major victory last year when the Supreme Court overturned a ban on corporate spending in elections.

The flood of new money -- $190 million by conservative groups compared with $94 million from liberals -- helped propel Republicans to win back the House of Representatives and make major gains at the state level in November's mid-term election.

The state-level gains will have far-reaching implications as legislators undertake the once-a-decade task of redrawing political maps in accordance with new census figures, a highly partisan process.

In the winner-take-all, essentially two-party US political system, creating a district where just 55 percent of voters support one party is usually all it takes to guarantee a win.

So politicians seek to pack the support base of opponents in as few constituencies as possible or break it up so that they are in the minority in several districts.

Republicans have total control over the legislature and governor's mansions in 20 states while Democrats control just 11.

Curtailing collective bargaining rights for public workers unions will essentially cut them off at the knees and that will have significant consequences for Democrats, said John Brehm, a political science professor at the University of Chicago.

Unions were the only liberal groups to make the top 10 list of groups spending money on the 2010 election outside of the more regulated political party system, according to the Center for Responsive Politics.

"If the unions are now out of the game, it shifts over heavily for the Republican interests for 2012," Brehm told AFP.

Unions are also extremely successful at getting voters to the polls -- a key factor in the United States where turnout reached just 41.6 percent of eligible voters in the 2010 mid-term election and 62.2 percent in the hotly-contested 2008 presidential election.

The mobilization power of unions was vividly apparent this week as tens of thousands of people flooded Wisconsin's state capitol to protest a bill aimed at busting public service workers unions.

Newly-elected Republican Governor Scott Walker was unbowed by the days of mass protests and insists that the only way to get his state's finances "on track" is to eliminate collective bargaining rights so public workers can't fight pay and benefit cuts.

Fighting unions is "almost an article of faith" for Republicans who see them as "a block in the path of capitalism," said Ken Janda, emeritus professor of political science at Northwestern University.

And the current budget crisis facing state and local governments gives them political cover and support from anxious taxpayers at a time when nine percent of Americans are unemployed and private sector workers have seen wages fall and benefits slashed.