Good morning Michael,
I'm Doug, and I'm very sorry to hear of your situation.
Under CA law, it is illegal for either an employee or an employer to alter a time card such that it misrepresents the actual time worked by an employer. In fact it is a misdemeanor and an employer may be fined for violating the law.
Because the action of the supervisor---by law---is a violation, you have the right to report the violations to the CA Department of Labor and ask them to deal with the issue for you. Once you file the report with the government, you are protected by the law, and it will be illegal for the employer or your supervisor to harass, or in any way retaliate against you for having filed the report.
The employer has the right to record your work time---in fact they have an obligation to do that and to do it accurately. However, they also have a legal obligation not to make changes to the time card without your approval---unless the changes are to correct an error that you made. But I sense that the supervisor is not making changes because you have made an error.
Also know that under CA law, if you request of your employer---you must be given the opportunity to review your payroll records within 21 days of your request. So you may want to review your records for other unlawful changes which have been made.
Either way, you may file a formal complaint with the Department by using the form you can find here:
Alternatively, you may go to your local Department of Labor office and make a complaint in person.
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I wish you the best in 2013,