At issue are 14 negative mailings the State Republican Party paid to produce and mail on Swallow's behalf. This week, GOP Chairman Joe Cannon denied responsibility for the content of the direct-mail. But NRCC spokesman Bo Harmon blamed the state party. Cannon then refused to mail the final two pieces to voters.

Democrats argue the mailings -- which cost $110,000 to produce and mail -- exceed the Bipartisan Campaign Reform Act's limits on party contributions to candidates.

They allege the national Republicans and Swallow deliberately tried to hide the identity of the NRCC, the group that authorized the content of the mailings.

"The letter of this law and the spirit of this law are that you have to disclose who's doing what, especially when it comes to negative pieces," said Dunn, who sent a letter to the FEC requesting an investigation.

But Republican Party Director Spencer Jenkins says the Democrats' complaint is just a partisan ploy. He acknowledges the Utah GOP paid for the mailings and provided volunteers to stamp and sort them -- all "fully within the bounds of federal election law."

"The accusation the Democrats are making are unfounded," Jenkins said. "They just want to take another dig at Republicans."