Thank you very much for your clarification. I see now that this is a prevailing rate issue since you are working on a government contract.
That being the case, Labor Code § 1770 et seq. does mandate that you are paid the prevailing rate for your job classification.
If you believe that your employer misclassified you as a "soundman" when in fact your duties entitled you to classification as a "sound and signal technician," your recourse would be to file a complaint with the Department of Labor Standards Enforcement, which is presently charged with enforcing prevailing wage laws.
The DLSE will conduct an investigation into your classification to determine whether it is proper. Although you may be entitled to additional pay as a sound and signal technician, the rate of pay for such classification would be the rate published at the time the contract was awarded, not the rate presently in effect. (Labor Code § 1773.6) However, as this would still be more than your present rate as a soundman, it would likely be worth your effort to proceed forward with a DLSE claim.
To file a claim with the DLSE, visit this link: http://www.dir.ca.gov/dlse/howtofilewageclaim.htm
Regardless of the DLSE's determination, your employer will be legally prohibited from retaliating against you as a consequence of your complaint. Any such retaliation would give rise to an entirely separate claim for damages.
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