agree 98% - union friendly states have laws that don't allow an employer to say FOAD. They are forced to allow the union to come in and hold a vote and they must abide by that vote. It only has to be 50% to force the entire workforce into the union. It only takes one employee to get the union in the door.
A lot of southern (anti-union) states have right to work laws, employees can opt out of the union and tell the union to FOAD
Employers cannot retaliate against a worker for union activities.
Laws vary state to state so check your local listings.
I'm not aware of too many cases where a business was legally prohibited from re-locating their business though..