Ground owners that refused would have their contracts revoked, and would be replaced immediately.
Each contractor has their own employees who would have to be unionized on a contractor by contractor basis, effectively making it impossible.
And
@UnionStrong, while I am informed on this discussion because I was an Express courier for over 20 years involved in this situation, I do not claim to know everything. If I were to make assertions regarding UPS, and you corrected me, I would concede to your first hand knowledge.