By this logic, management doesn't share in the losses, either. But they are for damned sure collecting bonuses when times are good. Sounds to me like the union wants a piece of that same "times are good" action.
when they lost $38 billion the union workers didn't get bills in the mail instead of checks.
If management got bills in the mail, they shared in the loss. AFAIK, they did not.
Management only takes losses so far as they have equity stakes in the company, which is to say the extent to which they are owners. When GM lost $38 billion in a year the people who own the company took that hit.
That's why employees usually don't value ownership in a company, because it cuts both ways. A salary only deposits into your account.