IMO, unions have served their purpose, and in many cases laws (OSHA) are replacing what unions used to be needed for to protect employees. In some cases unions have obtained undeserved and unnecessary power. db said it the best.
Having said that, I was the mgmt rep at a 3300 person UAW shop. When given the assignment, I knew that the union could help, or hurt the process. The way to get anything significant done was to make the union my friend. Looking back, we had some old school UAW's that was skeptical of everything mgmt had to offer, and some very, very progressive young folks (my age anyway) that I knew could help make my job easier. For those of you familiar with GM's quality network of "joint processes" that's how we did QS.
The first thing I did was select an hourly lead auditor along with the salary auditor that was already in place. She became my best ally in the process. The best way so say it, is that QS made sure that employees had what they needed to do their job, which is something that the UAW was easy to stand behind. In my experience, I made the union my ally, and they were instrumental in the success. I'm sure its not the same everywhere, and I was able to rally the right folks.