I doubt they are bluffing.it's a negotiation, someone will always threatens something, even if they do go through with the bluff and go on strike, Tesla can always offer a better deal and put everyone back to work the same afternoon, I don't see a big deal here
You realized that Tesla recently cancelled all contracts (as far as possible) with other companies and wants Grohmann to work 100% for Tesla and that this is a main reason for the change of mentality among the employees?How many clients of grohman you think will be lost if they walk of the job?
I would say the EU is somehow in involved in this as well.