The usual rules apply for managing workers. Bust up unions, make them sign contracts that bond them to servitude and relinquishes all of their rights, etc. But once you have them through corporate doors, you'll have to maintain a divide and conquer strategy lest there be a peasant revolution amongst the low level workers.
Employees work on a need-to-know basis. Don't give them any more information than they need to complete their task. Discourage interaction amongst employees. They don't need to know about anyone else. In case they do start interacting, tell them to stop gabbing and get back to work. You don't want employees talking amongst themselves because that means that they are: a) not doing any work and b) potentially plotting ways to circumvent your authority.
Insert yourself into all employee interactions. Make sure no meetings are called except by you. You can't have employees congregating for any reason other than your approved reasons. We all know what happens when the commoners gather; letting the masses form groups (like unions, clubs, or social cliques) will only lead to long term uprising. Quash the potential danger early and maintain your tight grip of the reins.
Finally, extinguish the spirits of the workers. No one likes perky employees. Happy workers are more likely to interact. Isolate these problematic workers and do everything you can to stamp out their happy demeanor. Somber, emotionless employees naturally maintain their isolation and obediently work without complaint. These are your ideal employees.
Your employees can hurt the company with a mass revolt. You can't beat back the superior numbers, but you can certainly keep them controlled. Divide them first, and the conquering will be easy.