One major thing that has to be done is to build up on the positives.
Remember this, you cannot use the old Carrt & Stick method if you don't have a carrot!
Personally I would take the time to sit down for just 5 minutes with each of these individuals and talk to them. Not necessarily to question them or push decisions in their face, but to understand them better.
I would also recommend finding an employee to bridge the gap between shop-floor and management. It helps a lot when bad decisions come up. They can provide you with inside information that you can use to your advantage too.
Find out why these guys are unmotivated. If they don't care and want to move on, put something together for them. If they are unmotivated because they feel un-valued ... put together something to make them feel valued. It sounds like the team spirit is broken, which happens in so many places. Build that up (not with cheesy team building crap though).
The best factory environment that I ever worked in was because the management rewarded the employees so well.
If production was good, our MD would purposely go into the bar where the workers were after work on Friday night and buy everyone there a couple of drinks, talk to them and thank them in person.
This kind of thing works better than classic motivation purposes, because it has a personal touch. Bonuses are nice, but the most impersonal way to reward.
Man management is the hardest thing, and I would say that before you wield your axe, or make negative decisions, build yourself up first. Don't walk in and be an ogre from the get-go that will be your image forever.
All in all, your best route is communication first, action later. Don't ever assume you know why your employees act like they do unless you ask them. Don't sit back and make decisions without communication first. Always try and get the other guy's angle. Motivate in a way that your employees actually ENJOY.
