The California Department of Industrial Relations website has helpful information:
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There are no laws which require an employer to provide vacation or sick pay benefits (except in San Francisco), so when an employer does offer such benefits, the terms of the benefit plan controls how they are earned and when they are paid. Typically, such plans are contained in employee handbooks or in employment offer letters.
It is not clear from your post if you are saying you were, in fact, paid sick and vacation in pay in advance of your having earned the right to take them. If I were you, I would ask the company for a copy of its policy pertaining to these benefits. If they do not have one, it would be very difficult for them to claim to have a legal basis for you repay them. It could be you actually did earn them.
By law, the employer must pay you all wages you have earned as of the last day of your employment. It cannot use self-help to deduct the money it is claiming you owe. If you run into continued problems with this employer, you should consult with an employment law attorney in your area, for more informed advice and assistance.
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I agree with my collegues. The main point is that the employer must pay you for all hours worked and cannot go back and deduct your wages. I agree that you need to get the specifics of the plan from the employer, that is your first step.