Legal Question in Business Law in California

It depends on your employment agreement. Even if you do not have a specific contract, you have some form of at least implied employment agreement which may have verbal terms, may include parts of an employee manual if you have one, etc. By law, only vacation time is "compensation" that must be paid at the end of employment if not used before then. Other types of leave are benefits that evaporate with the end of the job just like any other perk or benefit. However, some employers treat sick leave as compensation. Many union contracts make it compensation, especially public employee unions. So you have to look at whether you can find any proof that sick leave is treated as compensation in your job. If there is no written policy, either separately or in an employee manual, look at what has happened when people have voluntarily left the company, e.g., for another job. If they were paid for unused sick leave you have a good case that it is compensation. If they were not, then it is probably not payble if not used.