Which of the following is a reason an at-will employee cannot be discharged?

An at-will employee cannot be discharged for refusing to perform illegal acts because such a dismissal would violate public policy. The legal doctrine known as "public policy exception" protects employees from termination if they refuse to engage in illegal activities. This principle maintains that individuals should not be forced to act against the law, and firing someone for standing by their legal and ethical obligations reinforces the importance of compliance with the law in the workplace.

In contrast, other reasons for termination, such as poor performance reviews, taking too many sick days, or being absent from work, generally fall within the rights of an employer in an at-will employment context. Employers can terminate an employee for these reasons as long as they are not discriminatory or violating any specific legal protections.