Howard Dean's (search) presidential campaign wants to know exactly what rival Dick Gephardt's (search) campaign knows about a group that is running television commercials against the former Vermont governor.

Dean campaign manager Joe Trippi, in a letter to Gephardt on Wednesday, demanded that the Missouri congressman disclose whether he is associated with Americans for Jobs, Healthcare and Progressive Values (search). Several labor unions that endorsed Gephardt donated thousands of dollars to the group, whose two top officials have ties to Gephardt.

Gephardt said Tuesday he had no idea who was financing the group. His campaign has said it learned about the group from news reports.

"It's just a little too much of a coincidence here," Trippi said in a conference call with reporters. "That the campaign was totally in the dark is laughable."

Campaign finance laws prohibit federal candidates or their campaigns from coordinating with such groups, nicknamed "527s" (search) after the section of the tax code that applies to them.

Most of the group's ads have aired in Iowa, but its latest ad, broadcast in New Hampshire and South Carolina, features Usama bin Ladin (search) and suggests that Dean doesn't have the foreign policy experience to take him on.

Labor unions that endorsed Gephardt and donated to the group, including the International Association of Machinists, the Laborers International Union of North America and the Ironworkers Union, say they thought the commercials would be about Democratic issues.

"We did not think that it was money going toward any negative campaigning for another Democratic candidate," said James McNamara, a spokesman for the International Longshoremen's Association (search), which donated $50,000. "We believed the money was going to be used to promote Democratic principles, such as fair trade, worker's rights to strike, and health care."