Legal Question in Employment Law in California

There is a great deal of law on this question. So the answer is, "it depends." It used to be that you got vacation, sick days, or both, and life was simple. Vacation was considered earned compensation and could not be forefieted (though you could stop accumulating it if your employer had rules that you use it or stop getting more until you do). Sick pay was considered a benefit, since you could only use it if you got sick, which made it conditional. Sick pay could be use it or lose it. Now, however we have PTO and "personal days" and "comp time" and all kinds of other paid time off. The old rule still applies: if it is compensation it cannot be lost; if it's a conditional benefit it can. How to apply that rule, however, depends on the details of the employer's system of compensated time off.