It is labor's biggest priority for the new administration: changing federal law to make it easier for workers to unionize -- and win contracts with their employers.
Unions, which spent an estimated $450 million to help elect Barack Obama to the presidency and put more Democrats in Congress, want the Employee Free Choice Act passed quickly to begin to reverse decades of declining membership.
The U.S. Chamber of Commerce has vowed to spend $10 million to defeat the bill.
Obama's selection of union-friendly Rep. Hilda L. Solis (D-El Monte) as Labor secretary is seen as good news for the bill's advocates. She has called it "vital legislation."
Everyone agrees that the fight will be in the Senate, where the measure died last year after passing easily in the House.
Both sides plan to run grass-roots campaigns in key states and have begun airing TV ads, to "educate" the public.
The most controversial provision would require employers to recognize a union once a majority of workers signed membership cards, in what is known as a card-check system.
Companies can, but rarely do, recognize unions under those circumstances. Instead, they typically exercise their right to require an employee election organized by the National Labor Relations Board.
Trauma nurse Sherwood Cox, who worked to defeat two California Nurses Assn. drives at Western Medical Center Santa Ana, said that under the proposed law, he would be unable to keep the union out.
"When it's actually gone to vote, we've gone into the ballot booth and we've voted no," Cox said. "Both times, the union was totally shocked that they lost."
Under the card-check system, an employer could be surprised to learn that the workplace has gone union overnight.
Business leaders have couched the fight in terms of workers' privacy rights.
"The American public supports the secret ballot," said Randy Johnson, a vice president of the U.S. Chamber of Commerce. "Card checks are subject to abuse."
An ad produced by the bill's opponents features an actor from the HBO series "The Sopranos" portraying a mobster-like labor organizer threatening a worker to sign a union card.
"They're manipulating that," complained Josh Goldstein, spokesman for American Rights at Work, a nonprofit group that backs the bill. "Our battle right now, before we even get to the horse race on Capitol Hill, is how do we get people talking about this bill the way they should be?"
Card-check proponents have countered with their own television ad. It features a man dreaming of a benevolent boss, only to be awakened by his dog to go off to his presumably lousy job. Goldstein hopes that will get across labor's message: that unions give employees power at work, helping them obtain better pay and benefits.
Labor leaders say elections hurt unionization efforts because employers use the time leading up to the vote to harass, fire and threaten workers.
Melinda Burns said she was fired from her job after 21 years as a reporter at the Santa Barbara News-Press because she was a newsroom leader who brought in the Teamsters. An administrative judge with the National Labor Relations Board agreed, finding that she was among eight employees fired in violation of labor laws.
The newspaper's owner, Wendy McCaw, has appealed the decision. Management said the employees were fired for disloyalty or biased reporting.
"What we've learned is that you can break the labor law in America and get away with it for a long time," Burns said.
In fiscal 2007, the NLRB found that 1,771 employees were fired "in violation of their organizational rights" and it got employers to offer to rehire them. More than $124 million in back pay was awarded to the employees.
The proposed bill seeks to increase penalties against employers who violate the law -- its least controversial measure, though opponents point out that the penalties against unions would be unchanged.
Of more than 22,000 unfair-labor-practice charges filed with the NLRB in fiscal 2007, about 6,000 were against labor unions. Most alleged illegal restraint and coercion.
"In my campaign to convince people not to organize with the union, they put out a caricature of me as a puppet of management, with wooden legs and wooden arms and squashed nurses dripping off my shoes," said Cox, the Santa Ana nurse.
He said he fought the union because, as a sought-after trauma nurse, he doesn't need help from collective bargaining and doesn't want to pay union dues.
Union officials and nurses involved in the campaign denied sending out the flier with the caricature.
Even when a union is approved through an election, officials say, a hostile employer can drag out contract negotiations for years and ultimately petition to have the union decertified before one's ever signed.
Complaints of employers illegally refusing to bargain account for 60% of filings with the NLRB. The penalty for failing to negotiate in good faith is to be sent back into negotiations.