The company says the transferees are considered nonunion employees because they agreed to move to Milwaukee, where the Midwest mechanics are nonunion. Republic denies that it violated the Teamsters contract.
Interesting to see the contract. If, indeed, it says the IBT has exclusive jurisdiction over the Frontier aircraft it will be a tough sell by the company. But, it could say exclusive jurisdiction in Denver, or it could say Jurisdiction (non-exclusive). and other areas of their contract may say something else.
It would also depend on the way they were transfered. If they were terminated and re-hired it could be argued one way, just transfered another way.