Cal. FAM § 5603

(a) An obligor shall have 20 days after the service of notice of the registration of a California order of support in which to file a noticed motion requesting the court to vacate the registration or for other relief. In an action under this section, there shall be no joinder of actions, coordination of actions, or cross-complaints, and the claims or defenses shall be limited strictly to the identity of the obligor, the validity of the underlying California support order, or the accuracy of the obligee’s statement of the amount of support remaining unpaid unless the amount has been previously established by a judgment or order. The obligor shall serve a copy of the motion, personally or by first-class mail, on the local child support agency, private attorney representing the obligee, or obligee who is self-representing who filed the request for registration of the order, not less than 15 days prior to the date on which the motion is to be heard. If service is by mail, Section 1013 of the Code of Civil Procedure applies. If the obligor does not file the motion within 20 days, the registered California support order and all other documents filed pursuant to subdivision (a) of Section 5601 or Section 5602 are confirmed.

(b) At the hearing on the motion to vacate the registration of the order, the obligor may present only matters that would be available to the obligor as defenses in an action to enforce a support judgment. If the obligor shows, and the court finds, that an appeal from the order is pending or that a stay of execution has been granted, the court shall stay enforcement of the order until the appeal is concluded, the time for appeal has expired, or the order is vacated, upon satisfactory proof that the obligor has furnished security for payment of the support ordered. If the obligor shows, and the court finds, any ground upon which enforcement of a California support order may be stayed, the court shall stay enforcement of the order for an appropriate period if the obligor furnishes security for payment of support.