not completely the unions fault...its managements fault for giving into their demands and giving them the company...
the problem with unions is that you end up paying above market value and as a worker you forfiet your right to negotiate your own pay raise...so whether or not you deserve a pay raise no matter how you perform your going to get paid as much as the worst worker even if your the best
gm pays more for retired workers than regular workers and gm's costs are 60% more than toyotas...
this article talks about it in depth
http://www.heritage.org/Research/Economy/lm33.cfm