Democrat Tim Kaine suggested -- and Republican George Allen promptly rejected -- disclosing the identity of super PAC contributors.
Kaine's proposal came just a day after Politico reported that a super PAC was forming, aimed at helping Allen in his bid to return to the U.S. Senate.
Kaine first broached the subject in a December debate, when he pitched the idea of asking Super PACs to stay out of the race. This time Kaine wrote in a letter, "Let's adopt a simple rule: No Secret Money. Let's commit that any group running ads or conducting electoral activity for either of us should have to disclose their donors."
Allen must still win the GOP nomination but is expected to run against Kaine in what will be one of the most high profile and expensive Senate races in the country.
Allen was quick with his reply to Kaine's idea. Again by letter, he called Kaine's query, "an unfortunate gimmick, typical of the partisan gamesmanship playing out in Washington today."
Allen also tried to turn the tables, suggesting Kaine was "substantially funded by big union bosses." The Republican frontrunner suggested that Kaine should disavow a system that funnels union dues into campaign donations.
An attempt to have the last word came from Kaine's communications director, who wrote, "We remain hopeful that George Allen will reconsider and believe Virginia voters deserve nothing less than transparency."