If the employees are not interested, the employer is not interested, yet they are forced to do something they do not want (and which is voluntary, again by law) then it's not being "stubborn".
The union is doing this because they have members working for Tesla which has refused to sign a collective agreement for 5 years. Not all workers there have to want it, not even a majority.
Which the rules permit.
Being stubborn and winding up in the middle of a multi-union sympathy strike is similarly "entirely voluntary, by law".