I think that you are saying that Unions lost membership due to Republican legislation. The simple fact is that Unions simply went too far. I can remember, for instance, when GM went on strike over the fact that GM was unwilling to pay for magazine subscriptions for the washrooms. I have had my own problems with Unions so I can talk with some experience in that matter. I am not against them, when they make sense. On the other hand the Teamsters, for instance, didn't support their own membership, at the time, so much as demanding high fees for joining so that they could fund mafia casinos in Las Vegas. I actually had one business wherein the employees themselves choose to vote the Teamsters out. I suspect things have changed but, no longer being involved, I have no idea if they have or not.
The Unions had their problems to be sure. Many of them were just skimming operations for the union heads while cozying up to management. I've been in them and have nothing good to say about them. They are not all perfect but I would much rather work in a union than not. Workers tend to do better. Much better.
As far as Republican legislation you only have to look at one that spelled a steady decline for union membership: Taft Hartley
Combine that with the steady erosion of right to work laws (anti union organizing), management class demonizing them in the culture and media and a complicit Democratic party and you have what we have today. Stagnating wages over four decades, lowest labor uptake of GDP, lowest union participation, record high housing cost ratio to income, etc.
What's wrong with magazines in the bathrooms by the way? Is that so egregious as my state building a billionaire a new warehouse in NYC? The level of socializing profit to a small population of executives and shareholders these days is astonishing. But asking for education and healthcare? the public is somehow not there yet according to Democratic party leadership.