It never ceases to amaze me that once you get into records you see that it is not the case. That's costly in terms of credibility with the court system. Be consistent in applying this discipline in similar situations. Don't discharge employees for taking actions that they are required to take under law, or which are protected by public policy. These include filing a worker's compensation claim, serving on a jury, participating in the military reserves, cooperating with law enforcement officers in investigating another employee or refusing a supervisor's order to lie to a government agency.
Many states allow for high punitive damages.
People remember the last thing that is said to them longer than anything else. If you or a supervisor insults the employee during the termination proceedings, this could spark a wrongful discharge action. Treat the employee with dignity. I also counsel to give the employee a complete explanation as to why you are terminating, as opposed to staying vague and elusive. Hopefully they will then understand why you are doing what you have done, and reduce the likelihood of going to court.