Your employer's actions are illegal. An employer may not falsify or change time cards to remove hours worked so they do not have to pay you.
If the amount in question is worth your while to pursue, you should consult with an employment law attorney who handles wage and hour cases in your area, for advice on how to handle this situation.
Alternatively, you can file a complaint with the California Labor Commissioner. File the claim either by mail or in person with the Division of Labor Standards Enforcement (DLSE) office that handles wage claims for the city/location/community where the work was performed.
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 Avvo.com posting does not create any attorney-client relationship with the author. For specific advice about your particular situation, please consult with your own attorney.