Voter suppression by "Walker allies" or last-minute, uncheckable smear by Barrett people?

Salon reports:

With both sides counting on dramatic turnout, Tom Barrett’s campaign is charging Scott Walker supporters with dirty tricks. In an e-mail sent to supporters last night, Barrett for Wisconsin Finance Director Mary Urbina-McCarthy wrote, “Reports coming into our call center have confirmed that Walker’s allies just launched a massive wave of voter suppression calls to recall petition signers.” According to Urbina-McCarthy, the message of the calls was: “If you signed the recall petition, your job is done and you don’t need to vote on Tuesday.”

Last night I talked to a Wisconsin voter who says she received just such a robo-call. Carol Gibbons told me she picked up the phone and heard a male voice saying “thank you for taking this call,” and that “if you signed the recall petition, you did not have to vote because that would be your vote.”

There's a dirty trick in here somewhere, but whose? Somebody said she received this junk? Prove it. Who was it from? All the Barrett campaign is on the hook for saying is that they've heard reports from people who say they've gotten these calls. Why would Walker people do this? They aren't the desperate ones.

Urbina-McCarthy’s email requested donations to fund a new round of phone calls to all recall petitioner signers to make sure they know they still need to vote. 

Oh, they raised money off this completely deniable allegation?

Reached over e-mail, Barrett spokesperson Phil Walzak said, “If true, this shows the desperation of Walker and his right wing allies in the final hours of the campaign, and the depths to which they will sink to maintain their grip on power at the expense of the people and values of the great state of Wisconsin.”

This shows desperation, all right, but the Walker campaign isn't the one that's desperate. I love the egregious deniability here: If true... Great intro phrase for the sleazy rumor-mongers of the world.

ADDED: David Prichard — a journalism professor at U.W.-Milwaukee — has this May 2012 article in Wisconsin Lawyer about prosecuting false political speech in Wisconsin:

Wisconsin has three misdemeanor statutes that may be used against people who make intentionally false statements in political campaigns. The statutes prohibit false representations affecting elections, criminal defamation, and giving false information for publication. This article reports how the Wisconsin statutes have been used – and, in some cases, misused – over the past two decades....

Political speech is not automatically protected by the First Amendment. Intentional, calculated lies may be punished; at least 17 states have laws that forbid various kinds of false campaign speech. But the wisest course of action is to save criminal prosecution for the most egregious cases. The statutes discussed in this article should never be used against a sincere critic, a confused or careless partisan, or the perpetrator of a juvenile prank.