Doesn't work that way. UAW contracts are with the auto company, not the plant. If the company opens a new plant. like GM did with Toyota in California, the workers are automatically part of the company contract that says the UAW represents all of the workers except for the exempt (bosses) and non-exempt (clerks) workers.
Renault discovered that they could not "runaway" from the union after they bought "Mack" and built a new plant in North Carolina. Renault fought that clause in the contract in federal court because NC was a "right to work" state but they lost.
The Governor at the time said inviting Mack down here was the worse thing I ever did, after he lost the next election. The reason was all the other non-union skilled workers around the Mack truck plant like electrician, carpenters, machinists etc. started to join unions and got raises, benefits and better working conditions, after they saw what Mack was paying down the street for the same type of skills.
Even the waitress all around the plant in Willingborough loved the union guys. The Mack workers, that came down from Pennsylvania were giving tips in dollars while the locals were tipping with quarters
You might ask the Toyota workers in the California plant if they would prefer to work in any of the other non-union Toyota plants LOL
mike