The most heated battle in Congress -- and there are many at the moment -- may be over legislation that is not even on most Americans' radar screens: the Employee Free Choice Act.

Yet it's so important to unions and business that both sides are spending tens of millions of dollars to see that the legislation goes their way.

Take a guess at who is for it and who is against: Business groups call the legislation "Card Check" in their advertising and evoke imagery of tough "union bosses," while the labor movement calls the legislation by its uplifting title, the Employee Free Choice Act, and uses ads featuring cigar-smoking fat-cat CEOs.

The public relations battle is focused on whether the proposed legislation would take away the power of workers to hold a secret ballot election to decide whether they want to join a union.

Under existing law, if 30 percent of employees at a workplace want a union, an election is conducted by the National Labor Relations Board. That would still be true under the proposed legislation, but, if a majority of employees signed union cards, the union would automatically be certified.

In 66 percent of all National Labor Relations Board elections in the first six months of 2008 (the latest information available), workers voted to join a union. However, there are often lengthy battles involving employers, the labor relations board and the courts before an election is held.

Currently about 16 percent of American workers are unionized.

"We're not taking away workers' rights to have an election," said Jack Shea, president of the Allegheny County Labor Council. "I don't know why you would, but it's the workers' choice, not the management's -- and it's not the union's, either."

The U.S. Chamber of Commerce has been putting on a full-court press to defeat the measure, including newspaper and television advertisements, and efforts to have members write letters to their representatives in Washington, D.C., urging them to defeat the measure.

Glenn Spencer, executive director of the Workforce Freedom Initiative, the chamber's effort to defeat the legislation, said there have been breakfasts and speeches all across the country that all end with specific instructions on how to help defeat the bill.

Before the 2008 election, the chamber and business interest organizations campaigned actively for Republican candidates who were against the act. Since the beginning of the year, they have continued the campaigns against the legislation both in and out of Washington.

Mr. Spencer said the card-check provision is anti-worker because once unions get more than 50 percent of the workers to sign cards, the union has to be certified.

The 1,329-word bill, which was introduced to both the House and Senate on Tuesday and could come up for a vote as early as May, is about more than organizing a union.

A key issue under all the rhetoric is a provision in the bill that forces employers to agree to labor contracts.

If the act is approved as it stands, once a new union is certified by the National Labor Relations Board, both sides would have 10 days to start collective bargaining and 90 days before one side or the other could ask the Federal Mediation and Conciliation Service to step in to help reach an agreement.

If, 30 days later, there is still no contract, the mediation service could refer the matter to binding arbitration. And that really concerns critics of the bill.

"This is the union bosses' stimulus bill," Mr. Spencer said. "No matter what kind of ridiculous demands they put on the table, they will always get a contract."

He said, since the arbitration is binding, workers wouldn't get to vote on that initial contract, which would be in effect for two years. He also said having an arbitrator who doesn't understand a business decide what would be in effect a two-year contract could kill a business.

Mike Stief, a labor attorney with Jackson Lewis in Pittsburgh who has spent 17 years representing employers, is concerned, too.

"Arbitration in the public sector is nothing new," he said, but in cases in which an arbitrator decides a contract, "It's the taxpayers who end up with that burden."

Not surprisingly, others see it differently. Lawrence Mishel, president of the Economic Policy Institute in Washington, D.C., said the point of the arbitration is not to get a ridiculous unworkable contract but to encourage both sides to hammer out a deal before they have to go into arbitration.

Mr. Mishel said if the union and management are both bargaining, they can agree to put off any of the provisions. Nothing in the law says an arbitrator must come in; it's just an option, he said.

The binding arbitration provision, supporters say, is meant to address the difficulties of working out a first contract.

Bill Samuel, director of government affairs for the AFL-CIO union, said even when a union is successfully organized, 40 percent of newly organized workplaces never adopt a contract.

Mr. Shea's take on it is that people don't join a union to be a member of the union, but join a union to get a contract with management.

"What they want to do is sit down across the table without fear of being fired and discuss their problems," he said.

The tactics that employers use to keep any contract from ever being approved are just a second battle in the war against having a union shop, Mr. Shea said.

"This arbitration provision only applies to the very first contract," Mr. Mishel said. He said the reason arbitration will work is that it will get both sides to come to an agreement before having to take that step

"Arbitration works in collective bargaining and baseball," he said.

The act's final provision calls for triple damages for workers if employers are found to have fired them for union organizing efforts.

The act states that if the National Labor Relations Board finds an employer has discriminated against an employee because of organizing or union efforts, the board is to award the employee back pay plus twice that in damages, or triple what that employee would have been paid.

There is also a provision in which the employer who is found to have committed unfair labor practices will be fined $20,000 for each violation.

Mr. Spencer of the Chamber of Commerce said the remedy currently is to award a wronged employee back pay instead of triple damages.

He also said he finds onerous a provision that calls for preliminary investigations of allegations of unfair labor practices against employers to "be made forthwith and granted priority over all other cases." That, he said, transforms the National Labor Relations Board from a neutral party into one that spends its energies investigating businesses.

"From top to bottom, this is just not a piece of legislation we can support," Mr. Spencer said.

Both sides are determined to prevail in the battle over the legislation.

Mr. Shea described the act as the most important piece of legislation to labor since the 1970s when Jimmy Carter was president. Then there was a movement toward union-organizing reform but it failed by one vote. This year, organized labor is determined to get the Employee Free Choice Act signed into law.

"This will level the playing field by letting workers, not their bosses, determine the process by which they will form a union," said Mary Beth Maxwell, executive director of American Rights at Work. "It's very clear that 2009 is the year we will pass the Employee Free Choice Act."

On the other side of the legislation, the U.S. Chamber of Commerce and other business groups are just as determined to make sure the legislation is killed.

As the message read in a chamber's ad to defeat the "Orwellian 'Employee Free Choice Act,' " the group will "bring small business and community leaders to Washington to protect workers' private vote and protect jobs from government-dictated union deals."