Although the Oregon Legislature passed a measure last year that prohibits counties from regulating GMOs, Jackson County was left out because the ballot measure was already in the works.
The ballot initiative, known as Measure 15-119, would require the county to hire enforcement officers and to confiscate and destroy GMO crops.
Opponents say the measure, if passed, could cost the county more than $200,000 annually in administrative costs.
Enforcement and remediation costs are more difficult to calculate. But a recent county analysis finds abatement, which includes plant testing, removal and soil remediation, could run between $300,000 and $1.7 million for a 20-acre parcel.
They also say that the proposed ordinance threatens farmers with hefty fines and could cost taxpayers.
Opponents have launched a campaign, Protect Oregon Farmers, to defeat the measure.
"To maintain a healthy and safe food supply and thriving agriculture economy, it’s important for Jackson County to embrace all forms of farming and ranching," opponents wrote on their website.
Among the crops in question, growers in the county produce GMO sugar beets for seed, GMO sweet corn, GMO field corn and GMO alfalfa.
But ballot supporters, GMO Free Jackson County, say GMO technology is "unwanted, untested and unneeded," according to their website.
Supporters also contend that growing GMOs requires more pesticide use and threatens to contaminate conventional and organic farms with potential pollen drift from genetically engineered crops.
They also say they're concerned about health issues surrounding GMOs, noting that several European nations require labeling of foods that contain biotech ingredients.
The ballot initiative goes before voters May 20.