Accusations of dirty tricks are rare in Oregon politics, but Ralph Nader's (search) presidential campaign has sparked charges and countercharges between his campaign and backers of Democratic nominee John Kerry (search).

Union officials who support Kerry accused Nader's backers this week of engaging in widespread fraud and forgery in gathering signatures to place Nader on the Nov. 2 ballot in this battleground state.

Nader's supporters countered that Democrats and their union allies are resorting to "gangster" tactics by bullying and intimidating signature-gatherers in hopes of thwarting Nader's petition drive.

Nader, a 70-year-old consumer activist, is in a last-ditch effort to qualify for the ballot in Oregon, a state that once was one of his strongholds. He failed during two separate attempts to collect the 1,000 signatures needed to qualify for the ballot and now is trying another tack — gathering 15,000 signatures statewide. Nader has until Tuesday to collect them.

But as the deadline nears, the tension between his campaign and his opponents is growing.

The Service Employees International Union, which supports Kerry, said in an election complaint filed with the state that it has heard from more than 30 people who say their names were falsified on Nader's petitions.

The union also has warned nearly 60 of Nader's signature-gatherers that they could face a felony conviction and prison time for knowingly submitting fraudulent signatures.

"The evidence indicates a clear pattern of widespread signature fraud in the effort to put Nader on the ballot," union spokesman Mark Weiner said.

Nader's Oregon coordinator, Greg Kafoury, said one petition-gatherer was "badly shaken and intimidated" by two union members who knocked on her door and told her she was under investigation.

"We have been sabotaged and smeared, and now we have had our people bullied by people who knock on doors at night," Kafoury said. He said there is no intentional effort to turn in invalid signatures.

Kafoury said 30 of the campaign's 150 petition-carriers have quit because of the union's actions, but he said the Nader campaign still believes it will be able to meet Tuesday's deadline.