Do I have a case for defamation of charater or other things?

Recently a couple of fellow employees and I have been socializing in the parking lot at our place of employ on our breaks and lunches. Yesterday my friends supervisor threatens him and my other friend to be "written up" and an turn possibly terminated for alleged drug use on the premisis. This satement is completly false as none of us have ever done any drugs in our lives. However Apparently rumers were started and this supervisor is threatening to give corrective actions for a false accusation. I am under another suervior so I may hear about this and be threatened as well. Both of our superisors seem to have a great deal of contempt for us as employees and are constantly threatening to write us up and telling us how they can get us fired at any time they want to . i.e. flaunting their authority. We are upstanding employees with a good ethic and this is creating a hostile work invironment of sorts. One such encounter involes the same friends supervisor threatining wiht yet another write up for an action that was again falsely accused and it involes a statement of "do not cross me, last month in a five day period i have 8 people fired [large employee base] and if i want an employee gone they are gone!)

This is very disastisfying as a work environment. Do we have any type of lawsuit available to us if need be?