In what is set to be their first major showdown since Democrats took control of Congress, business and labor interests are poised for a multimillion-dollar clash over a measure to make it easier for workers to unionize.

Deep-pocketed corporate lobbying groups have joined together to defeat the proposal, today announcing the launch of a new coalition to coordinate their activities. The effort, called the Coalition for a Democratic Workplace, has the backing of the U.S. Chamber of Commerce, the National Association of Manufacturers and the National Federation of Independent Business, among others.

Facing them is an informal alliance of labor groups, headed by the AFL-CIO and the breakaway Change to Win unions, working across a divide in the labor movement to advance the measure. They also have the backing of Americans United, a liberal group closely aligned with Congressional Democrats.

At issue in the fight is the Employee Free Choice Act. A top priority for labor unions and Democratic leadership, the bill would allow employees at a workplace to organize once a majority sign cards indicating they want to join a union.

Labor officials say the issue is about economic fairness, arguing corporate intimidation has contributed to a decades-long slide in union membership, which in turn has frozen workers out of improving economic conditions. Businesses counter that replacing the current system of secret-ballot votes will violate workers’ privacy and expose them to bullying by union organizers.

With union membership continuing to drop — it fell to 12 percent of all workers last year from 12.5 the year before — the issue is gaining urgency in the labor movement. Labor unions, which provide critical help funding Democratic electoral efforts, reportedly signed up 150,000 new members last year using the card-check elections.

Under the bill, workers could pick whether to unionize through card checks or secret-ballot elections, and their employers would be bound to recognize the result.

The bill, set for markup today in the House Education and Labor Committee, is expected to cruise to House passage next month. It already claims 234 cosponsors, including seven Republicans.

Senate Health, Education, Labor and Pensions Chairman Edward Kennedy (D-Mass.) hopes to introduce it early next month, and labor lobbyists said they are already working to line up a majority of Senators to sign on. But even though they got a jumpstart pushing the bill — kicking off their drive in December with a Capitol Hill press event featuring Kennedy and House labor panel chairman George Miller (D-Calif.) — labor lobbyists acknowledge they face tough odds.

For starters, rounding up the 60 votes needed to end a filibuster could be difficult. “It’s a challenge,” said Bill Samuel, director of legislation for the AFL-CIO. “We hope that a strong House vote will convince Senators this is the right thing to do.” Even then, President Bush is expected to veto the measure.

The battle will be joined next week when lawmakers head home for the Presidents Day recess.

The AFL-CIO plans to target 90 Congressional districts, mostly to shore up support for lawmakers who have indicated they will back the measure. About a dozen of their targets will be Republicans so far undecided or opposed.

Americans United will take on an additional 15 to 20 GOPers who have lined up against the bill, spokesman Brad Woodhouse said. “Our view is that the folks within the labor community can hug their targets,” he said. “On the other hand, we want to thump those that don’t do the right thing.”

Officials with the Coalition for a Democratic Workplace declined to discuss specifics of their plans for the break, but said they will tap the state affiliates of their member groups to start reaching out to members. “We’re going to be very active in the field over the next few weeks. And we’ll begin the education campaign as Members return home,” said Danielle Ringwood, a member of the coalition’s management committee and lobbyist for the Associated Builders and Contractors.

The business-backed group launches today with a Web site (www.myprivateballot.com) and polling information supporting their position. At the House markup today, coalition representatives will hand out fliers featuring a photo of a toilet, and inset, a voting booth, with the tagline: “Some things are designed for privacy. Here are two of them.”

The group has tapped Todd Harris, a partner with the all-Republican firm DC Navigators and a former aide to former Florida Gov. Jeb Bush (R) and Sen. John McCain (R-Ariz.), to head up its media and lobbying strategy.

In the face of the daunting tally of co-sponsors, coalition leaders said they are not going to concede the House vote. Instead, they are aiming to find signers whose support is soft. “A lot of Members have signed onto this bill without really grasping what they’ve co-sponsored. Our task as a coalition is to educate them and help them understand they’ve been sold a bill of goods,” said David French, another coalition manager and lobbyist with the International Franchise Association.

But a House Republican aide said for GOPers and their allies, the best hope “is to extract as much blood as possible through the debate, and then let the Senate weigh in from there.”

The foes are concentrating on field work for the meantime, but both sides said they plan to be on the air with ads as the fight moves to the Senate. And they each pledged they have the resources to keep up the fight for a long time — into next year and beyond if necessary.

For support, Americans United is calling on groups that lent money and organizational strength to its Change America Now campaign, which backed up the economic pieces of House Democrats’ “100 hours” agenda. That group is still focused on final passage of a minimum wage hike, but with House Democrats pivoting to regular order, Woodhouse said the employee card-check bill will become a top priority.

“It fits nicely into the broad spectrum of issues we’re pushing to relieve the middle class squeeze and create a better balance in the economy between the most productive workforce in the world and corporate executives and managers,” he said. “This may be a longer-term process. But if Republicans obstruct this, then part of what we do is make sure they pay a price with the public.”

Harris said his group is just getting started.

“We’re literally in the process of getting the curtain open on this thing. Over the next six months to a year, you’re going to see the coalition highlighting not only the impressive group of organizations that are supporting us but making sure people understand that underneath this fight in Washington are real lives, and real workers whose right to privacy is going to be stripped away should this bill pass,” he said.