Measure 82, on the May ballot, would replace the weight-distance tax with a 29-cent diesel tax and a 5-cent hike in the gasoline tax.
Backers of the plan are suing AAA for spreading false information. At a news conference this week, AAA said two new studies show motorists would pay $100 million more a year, while big trucking companies would get a $50 million break. The studies were conducted by Willamette University and Portland State University.
"No wonder trucking interests plan to spend $4 million to jam this down people's throats," said Roger Graybeal, president of the Oregon-Idaho chapter of AAA.
The coalition supporting the measure points to a recent report from the nonpartisan Legislative Revenue Office, which found that while cars would pay more under the plan, so would trucks.