It depends on the specific language of your employer's sick leave policy. California employers are not required by law to provide sick leave. Those that do have the discretion to establish which employees are eligible, how much will be allowed, the manner in which it will accrue, and whether it will be paid. However, if your employer has consolidated sick leave (along with other types, such as vacation and holiday leave) into an all-encompassing paid-time-off (PTO) benefit scheme or allows you to use sick leave for whatever purpose you desire, then your sick leave would be subject to the same rules as vacation leave--meaning that it would vest as it is earned (i.e., your employer would not be able to take it away, legally speaking).
If you believe your employer has broken the law, you should file a claim with the Labor Commissioner. You can get more information about this here: http://www.dir.ca.gov/dlse/HowToFileWageClaim.htm.
Most likely yes. An employer is not required by law to provide paid sick leave. Does your employer have a consolidated sick leave, vacation and personal leave in a PTO (paid-time-off) policy?
Unless sick leave is defined as part of PTO, sick leave does not accrue.
Frank W. Chen has been licensed to practice law in California since 1988. The information presented here is general in nature and is not intended, nor should be construed, as legal advice for a particular case. This posting does not create any attorney-client relationship with the author. For specific advice about your particular situation, consult with your own attorney.