The proposed seven-year deal will freeze their pay, slash hundreds of jobs and assign large volumes of work to nonunion workers.
Dozens of union members milled around outside the Waukesha County Exposition Center on Monday where the vote was taking place, some expressing anger over the motorcycle maker's contract demands.
'For Sale' signs hung on about a dozen of the approximate 100 Harley motorcycles parked outside the center.
Harley-Davidson executives say they will move production out of Wisconsin if the contract is rejected. That would eliminate about 1,350 jobs.