Classic prisoner's dilemma problem there. If the union negotiates good working conditions, benefits, hours, and wages and I don't pay, then I got something for nothing. If they can't and I did pay, then I have completely wasted the money spent on dues. Either way, I as an individual am better off not paying dues. And thus, we all think that way, the union dies, and we all get a much worse deal than if we all cooperated. Gotta love divide and conquer whether you're going to war, sorting an array, or screwing labor over.