5%? Never. The assumption is that it would remain a minority, which is easily managed through corporate policy.
I'm asking what the plans are when the 5% becomes 25%, 45%, etc.
No plans, they just assume that it will never happen, if it does happen they will concede temporary defeat and pretend that everything is fine, let all of you back in and lull you into a false sense of victory, then when the time is right they will strike down on you with great fury and vengeance, one by one. They won't fire everyone, just enough of you to send a good message.
There are so many things we get away with that are never enforced, no one cares when I am 20 minutes late from lunch, no one cares that I sometimes use the employers water to wash my car, but wait until they are out to get you, you won't survive.
What the unions are often helpful with is that they know a lot of things about a lot of people, for an example my manager usually goes to fetch the kids during the day while he's supposed to be working, he sometimes use the employers printer to print his kids school stuff, so everyone knows everyone's dealings and everyone is on the same page.
That's how everyone coexist, don't bother us and we bother you, that is the kind of the prevailing environment, knowing people and blackmailing you if necessary is all part of the game if the situation calls for it. In other environments management has the upper hand on everything because employees think they are educated so nothing will happen to them.