Accusations of voter fraud have hurled a giant mud ball into an already messy presidential campaign, with Republicans alleging that Democrat Barack Obama has close ties to an activist group accused of compiling fake registration forms, including ones for the starting lineup of the Dallas Cowboys – submitted in Nevada.

Rick Davis, the campaign manager for Republican candidate John McCain, told reporters in a telephone conference call Friday that Obama's connections to The Association of Community Organizations for Reform Now, known as ACORN, should be investigated. The group says it has signed up 1.3 million poor and working-class voters in a mass registration drive in 18 states this year.

Some of those registration cards have become the focus of fraud investigations in Nevada, Connecticut, Missouri and at least five other states. State investigators this week raided ACORN's Las Vegas headquarters, seizing documents and computer data as part of a probe into scores of fabricated registration forms, including those signed in the names of Dallas professional football players.

But two hours after the McCain campaign teleconference Friday afternoon, ACORN held one of its own and accused Republicans of playing dirty politics and of trying to keep America's less fortunate voters, who tend to be Democrats, from the polls on Nov. 4.

“If you can't stop the 1.3 million people from getting on the rolls, at least shoot the messenger,” said ACORN spokesman Brian Kettenring. “There is absolutely no doubt in our minds that the attention being paid by the right is tremendously disproportionate to the problem.”

McCain, trailing Obama in recent polls, called Thursday for a federal investigation of ACORN during a campaign rally. In a series of teleconferences this week, the Republican National Committee accused the organization of deliberately forging registration cards and called the community group “a quasi-criminal organization.”

Obama and two other lawyers in 1995 represented ACORN in a lawsuit against the state of Illinois to make voter registration easier. During this year's primary, Obama hired a firm with ties to the group for a massive get-out-the-vote effort.

In response to salvos from the McCain campaign, Obama's team shot right back, calling the attacks “false claims (that) are nothing more than another dishonorable, shameful attempt to divert voters' attention from the unprecedented challenges facing their families and our nation,” spokesman Tommy Vietor said.

ACORN assists working-class and lower-income people on issues including housing, credit, education, and subprime lending. Founded in 1970, it claims 400,000 members across the country.

The group is familiar with fraud allegations – since the 2004 election, ex-employees in states including Florida and Missouri have been convicted of submitting bogus registrations.

Organization officials blame those incidents on cheating and lazy workers who wanted money for doing no work – and were fired. ACORN canvassers are no longer paid a fee for every card delivered. Current field workers receive an hourly wage, said executive director Michael Slater.

He also said that most wrongdoing is discovered by the group itself, when employees examine registration cards submitted from the field. Problem cards are flagged and turned over to local election officials, Slater said. Most states, he added, require that every collected card be given to voting jurisdictions.