It is illegal to label a potato as an 'Idaho Potato' if it was grown out of state.

The Law

You cannot slap the prestigious 'Idaho Potato' label on a spud cultivated in neighboring Washington or Utah. The Idaho Potato Commission fiercely guards its trademarked agricultural crown jewel, treating potato fraud as a serious legal offense. Violators face steep fines for attempting to pass off inferior tubers as the genuine, volcanic-soil-grown article.