California Code, Code of Civil Procedure - CCP § 706.077

(a) Subject to subdivision (b), an employer upon whom a withholding order for taxes is served shall withhold and pay over earnings of the employee pursuant to such order and shall cease to withhold earnings pursuant to any prior earnings withholding order except that a withholding order for support shall be given priority as provided in Section 706.030. When an employer is required to cease withholding earnings pursuant to an earlier earnings withholding order, the employer shall notify the levying officer who served the earlier earnings withholding order that a supervening withholding order for taxes is in effect.

(b) An employer shall not withhold earnings of an employee pursuant to a withholding order for taxes if a prior withholding order for taxes is in effect, and, in such case, the subsequent withholding order for taxes is ineffective.