Cal. Family Code § 5270

(a) An obligor may move to quash an assignment order on any of the following grounds: (1) The assignment order does not correctly state the amount of current or overdue support ordered by the courts. (2) The alleged obligor is not the obligor from whom support is due. (3) The amount to be withheld exceeds that allowable under federal law in subsection (b) of Section 1673 of Title 15 of the United States Code. (b) If an assignment order is sought under Article 3 (commencing with Section 5250), the party ordered to pay support may also move to quash the service of the order based upon Section 5260. (c) The obligor shall state under oath the ground on which the motion to quash is made. (d) If an assignment order which has been issued and served on a prior employer is served on the obligor’s new employer, the obligor does not have the right to move to quash the assignment order on any grounds which the obligor previously raised when the assignment order was served on the prior employer or on any grounds which the obligor could have raised when the assignment order was served on the prior employer but failed to raise.