I understand what you're saying, but walking out or forcing negotiations during a global pandemic is sociopathic, and the union would gather a massive amount of political venom.
I don't know how you think bargaining works, but they don't just demand "do XYZ or we'll all walk out". There's lots of levers on both sides. The point of negotiation is to arrive at a mutually beneficial solution. Striking is always a last resort, and quite rare, since it's bad for workers, too.
