Let's say I have a company with an R&D budget of $1 billion. $100 million goes into robotics and AI, $900 million goes into core business interests. You form a union and demand all kinds of ridiculous accommodations that you could never have reasonably asked for on your own.
What will happen when budgeting for the next fiscal year? Replacing you is a core business interest now, and so is avoiding the need to hire your replacement. The R&D budget will be adjusted accordingly.
If you want "leverage," the best way to achieve that is to make yourself more valuable, not less.
Surely there is some room there. If the cost of labor were already equal to the cost of replacing the labor, then the employer might as well just replace them now. So it must be lower by some amount. The point of a union (it seems to me) is to capture a larger portion of that surplus, but leave the employer with enough that the arrangement is still worthwhile.
If you're unfamiliar, this is an excellent introduction to this concept: https://www.mrmoneymustache.com/2012/01/13/the-shockingly-si...
It's extremely simple. It's boring. It's slow (but much faster than the alternative!). And it works.