If you find a problem going on with two different employees, what would you do?

You should evaluate the problem first. Can this argument or disagreement be handled with a simple conversation? If so, you should try to de-escalate the situation. Also, evaluate whether or not this disagreement is impacting any customers. If it is, you need to diffuse the situation immediately. If this problem is beyond your control, you need to immediately tell a supervisor. If these employees are working together to steal company property, the managers need to know immediately.