It sounds like the biggest contention is just cause for terminations instead of at will. If the employer normally isn't firing people without a good reason it sounds like an easy win. Why do they fight these negotiations so much?
Isn't this the default state of affairs for american private enterprise? This is why PIPs are so wildly popular—it's trivial to fabricate performance reasoning regardless of the actual motivations for firing.
Granted, I don't see how you could negotiate your way out of this. We need federal labor protections to make serious movement on this.