An employee can be fired for not reaching sales goals, for any reason, or for no reason at all. That is unless doing so would violate the terms of an employment contract or union agreement. Also, their treatment must not constitute some form of legally actionable discrimination. However, as to the latter, not all employees need to be treated the same or even fairly unless they are in a legally protected class. This means that they cannot be given treatment that differs from that of their co-workers unless it is due to their race, religion, national origin, disability, gender, age (over 40), etc. Bottom line, in an at-will employment relationship, a company can set the conditions of work much as it sees fit.