California is an “at will” state, which means an employer can fire an employee for any reason or for no reason at all - even if they simply do not like them. However, they cannot fire an employee because they are a member of a protected class. In other words, it is illegal for an employer to fire an employee for any reason connected to their gender/sex, race/color, disability, age, national origin, pregnancy/breastfeeding, or sexual orientation. It is also illegal to terminate an employee in retaliation for exercising their rights, such as reporting or refusing to participate in illegal activity, reporting safety violations, filing a complaint, etc.