An anti-union group is urging the Federal Election Commission (search) to investigate one of the largest unions in the country, claiming the Service Employees International Union (search) unlawfully spent workers' dues to elect Democrats in last week's election.

The National Right to Work Legal Defense Foundation (search) said Wednesday that SEIU gave millions of dollars from members' dues to a partisan political group, America Coming Together (search), which in turn spent the money illegally to finance political campaigns through the Democratic National Committee.

The foundation complained that dues are required as a condition of union membership and cannot be spent on political campaigns.

"SEIU officials used the hard-earned wages of rank-and-file workers to bankroll the campaigns of hundreds of political candidates across America," said the foundation's president, Stefan Gleason. The group opposes mandatory union dues and provides free legal representation for members with allegations of union abuse.

SEIU was unaware of the complaint. "We are confident we are in compliance with the law," said spokeswoman T.J. Michels. "It's not surprising an anti-union group is making these allegations about a political mobilization spearheaded by thousands of SEIU members who want to put our country back on track for working families."

SEIU has said it was spending $65 million on the election.

The FEC can take years to resolve such complaints.