"This is a serious matter, and I'm calling him on it," Kucinich, an Ohio congressman, said in a telephone interview Friday. "Whispering, trying to rig an election, then denying what's going on and making excuses. It all reflects a consistent lack of integrity."
Kucinich's comments came after Edwards and Hillary Rodham Clinton were overheard Thursday discussing the possibility of limiting the number of participants in future presidential forums.
In an exchange captured on camera and open microphone by broadcasters after an NAACP forum in Detroit, Edwards approached Clinton onstage and whispered in her ear.
"We should try to have a more serious and a smaller group," Edwards said, and Clinton agreed.
"Our guys should talk," Clinton said, complaining the format had "trivialized" the discussion.
Kucinich, who typically polls in the low single digits, clearly felt the slight was directed at him. All eight Democratic contenders took part in the program, including Barack Obama, Bill Richardson, Chris Dodd, Joe Biden, Mike Gravel and Kucinich.
Both Edwards and Clinton were asked about the exchange Friday, and offered different explanations.
In New Hampshire, Clinton seemed to lay responsibility on Edwards.
"I think he has some ideas about what he'd like to do," she said, adding she liked participating in the forums.
For his part, Edwards told reporters in Iowa that he wasn't in favor of barring anyone from future gatherings. Rather, he said he wanted to see them separated into two groups of four each, chosen randomly.
"The result would be that we would have a much more serious discussion and people would actually be able to see what the differences are between us," he said.
Kucinich called Edwards' explanation "disturbing" and said he planned to contact Edwards and Clinton immediately to demand an apology.
"I accept their offer to participate in a debate with just the two of them," Kucinich said. "John should be happy with this, since he wants a small group."
Kucinich's bitterness toward Edwards was somewhat ironic, given the boost he gave Edwards in Iowa when they were both running for president in 2004.
Kucinich, who is very popular with a small but ardent group of liberal activists, asked his Iowa supporters to back Edwards if they didn't meet voting thresholds in any of the state's precincts. That effort increased Edwards' final delegate count in the state, putting Edwards within striking distance of winning the caucuses that year.