Business and labor groups have taken last year’s expensive lobbying fight over secret ballots and unions to campaigns across the country, as both sides highlight research suggesting candidates would be better off embracing their positions.

A coalition of business groups is pressing a new poll that concludes Sens. Norm Coleman (R-Minn.) and Susan Collins (R-Maine) could be boosted by their votes last year against the Employee Free Choice Act (EFCA), which would allow workers to form unions without a secret ballot. Both are seeking reelection this year against tough Democratic opponents.

CDW’s results show that 41 percent of households in Minnesota and 44 percent in Colorado are “less likely” to vote for a senatorial candidate who supports the EFCA. Only 13 percent in Colorado and 11 percent in Minnesota feel “more likely” to vote for a supporter of the act.

Labor groups dismiss that poll, and are pushing their own research that says EFCA support will help candidates in the fall. They say McLaughlin & Associates , which is led by a Republican pollster, posed questions in a way that would make respondents skeptical of EFCA’s merits.

“The questions [in CDW’s poll] are loaded questions to give a particular outcome,” said Mary Beth Maxwell, executive director of American Rights at Work , a nonprofit group that receives funding from labor unions. She said the CDW poll is getting little attention because it is not credible.

If EFCA became law, workers could form unions as long as a majority of employees sign cards designating a labor group as their bargaining representative. Business groups charge that this would eliminate the secret-ballot system, allowing union supporters to bully and intimidate workers into joining unions. Union representatives counter that the present system allows employers to get rid of union organizers and threaten and intimidate workers into voting against forming a union.

Both sides agree the bill would make it easier for workers to unionize. Since unions are a consistent financial backer of Democratic campaigns, increasing their membership would favor that party.

The House approved EFCA in a 241-185 vote in 2007, but the measure failed to get enough support in the Senate to break a filibuster led by GOP senators. Every Democratic senator with the exception of the absent Sen. Tim Johnson (S.D.) voted to proceed to the bill. Sen. Arlen Specter (Pa.) was the only GOP senator to vote in favor of moving forward.

Democratic leaders are expected to bring the bill up again in the next Congress if they maintain their majorities. If a Democrat is elected president, a handful of Senate Republicans could be the last barrier to the measure becoming law.

Both Sens. Hillary Rodham Clinton (N.Y.) and Barack Obama (Ill.), the two Democrats battling for their party’s nomination, voted for EFCA last year, while Sen. John McCain (Ariz.), the presumptive GOP nominee, voted against it.

The CDW poll suggested union households were less likely to support candidates if they favored EFCA, a conclusion disputed by labor. In union households, 37 percent in Minnesota and 44 percent in Colorado said they were less likely to vote for a candidate who backed EFCA. Only 20 percent of the union households in Minnesota and 11 percent in Colorado were “more likely” to support such a candidate.

The business group highlighted that 80 percent of those polled agreed that secret-ballot elections “are the cornerstone of democracy and should be kept for union elections.” Four hundred union and non-union households were polled in Colorado and Maine, and 500 in Minnesota.

“It’s clear that opposing the private ballot for workers is a political liability for candidates, particularly those running in tight races,” said Brian Worth, vice president of the Independent Electrical Contractors Inc. and a member of CDW, in a press release.

Stewart Acuff, organizing director at the AFL-CIO, said other research suggests Americans will back politicians who support EFCA.

“Our polling indicates 69 percent of Americans think workers should have the benefits of legislations like the Employee Free Choice Act,” Acuff said.