Unions in Michigan manufacturing (and Illinois too) already have 2 tier wage schemes. The older guys keep the benefits and wage scale (adjusted for inflation) that they had in the height of union power, the 80s.
The young men are basically paid less net than southern RTW states, if I recall the numbers correctly.
My experience is that union pay is really not the biggest deal killer, especially now with the 2-tier contracts. Its the constant fighting. It turns into a situation where both sides, the worker and the management, do only absolutely the bare minimum for each other, no compromise and hardball 100% of the time.
Worker does the bare minimum - "not my job, I won't do that extra thing you asked." "Its not in the contract" "hey engineer, you can't touch that thing, that is my job and only I can do it." etc
or "Oh some of us are getting laid off because 2009 crash; lets sabotage $60k in equipment."
Business does the bare minimum - "we could give you a bonus for a good year, but its not in the contract" "slight downturn in the economy? lets layoff 3x as many people as we project having to cut just to be sure because that is what the contract allows" "can we negotiate the worst possible contract for the union? if they agree to it, lets do it"
Going from our Illinois plants to our southern state plants, the attitude difference is night and day. Trying to fix something to make the plant run better, goes something like this...
Illinois - don't touch anything, don't ask anyone for help cause they don't want to do it, I don't care, thats your problem not mine 'buddy'. You need to get my supervisor to come here and tell me to change anything.
Southern US state, Japanese plant, South American plant, etc - Oh hi, how can we help? oh yeah, have you thought about doing this and that to fix this problem? yeah we can try that, lets set it up after break. Give me a second, I need to polish this oil smear off this machine.
Like I said, from my limited experience with manufacturing the union pay scale is not that hard to accept or budget. But its the constant battle to do anything, to be flexible in the slightest, and the absolute disgust the worker has for the company he works for that just makes it an anchor around the neck. And so it sets up a tit for tat exchange that has spiraled down to where we won't build another plant in Illinois or other northern states. Its just too expensive, and the cost has very little to do with pay scale.