Business and labor groups have brought hundreds of people to D.C. this week to rally for and against the Employee Free Choice Act, slated to be introduced Tuesday by Democratic lawmakers in both houses of Congress.

The SEIU today hosted protests outside eight major corporate industry associations that oppose the legislation. More than 300 workers from around the country were expected to participate, according to spokesman Jeff Cappella. SEIU's targets include the U.S. Chamber of Commerce, National Association of Manufacturers, National Restaurant Association, Business Roundtable and Retail Industry Leaders Association. The union supporters plan to meet with lawmakers on Tuesday to push the legislation.

EFCA would allow unionization if a majority of workers sign authorization cards and would eliminate a company's right to demand a secret ballot election. Proponents maintain that it allows workers to unionize more easily and freely, while opponents counter that union organizers will coerce individual workers to join and hurt small business.

These efforts come on the heels of AFL-CIO's winter meeting last week in Miami Beach, Fla., where both President Obama (via video message) and Vice President Joe Biden (in person) explicitly embraced the legislation.

SEIU's biggest rally today was planned for Lafayette Park, which borders the Chamber of Commerce's offices and the White House. This suits the chamber just fine, according to Justin Hakes, external affairs manager for the group's anti-EFCA campaign, the Workforce Freedom Initiative. "We're glad they're here," Hakes said. "First of all, it's exhibit A as to the kinds of pressure that individual workers will face if card check passes."

The chamber launched its own campaign this week by helping fly in 180 business leaders from across the country to meet with lawmakers. The group plans to follow up with TV and print advertisements in the business leaders' home states, and Hakes said the chamber will likely host a second round of guest advocates in April. The business group vowed to spend at least $10 million this year to fight the legislation, the Wall Street Journal reported.

                                                                                                                    --Amy Harder

Two of the act's main opponents -- the Employee Freedom Action Committee and the Center For Union Facts, both led by lobbyist Rick Berman -- are running TV and radio ads in states such as Nebraska, Arkansas and Colorado, which the groups deem crucial to the EFCA debate. In particular, the Employee Freedom Action Committee has been running an ad in the Washington area featuring former Democratic presidential candidate George McGovern, who says the bill "cannot be justified." McGovern has a "strong history of taking unpopular stances in his party that might have political ramifications," said Justin Wilson, managing director for both groups.

Lobbying doesn't come cheap, especially for an issue as contentious as EFCA. Hakes said the chamber raised and spent $10 million working against the legislation in 2008, including the official launch of its campaign in July. "We're expecting to at least double that this year," he said. Berman's groups have spent upward of $20 million advocating against the legislation throughout the past 14 months, Wilson said.

While Cappella didn't say how much the SEIU is spending on its efforts, he claimed it was far less than what was being spent by the other side. Today's rallies, in fact, are intended in part to protest the nearly $140 million the SEIU says its opponents have spent lobbying against the legislation. Josh Goldstein, spokesman for American Rights At Work, said his group has spent about $10 million since Labor Day. He acknowledged that it "doesn't compare with the business community, but that's not a goal of ours." He said the support in both chambers of Congress and the White House reflects the success American Rights At Work and other pro-EFCA groups have had.