(1) Service of the wage assignment order or income withholding order on the employer is invalid unless it is served with five answer forms in substantial conformance with RCW
26.18.120, together with stamped envelopes addressed to, respectively, the clerk of the court where the order was issued, the Washington state support registry, the obligee's attorney or the obligee, and the obligor. The obligee shall also include an extra copy of the wage assignment order or income withholding order for the employer to deliver to the obligor. Service on the employer shall be in person or by any form of mail requiring a return receipt.
(2) On or before the date of service of the wage assignment order or income withholding order on the employer, the obligee shall mail or cause to be mailed by certified mail a copy of the wage assignment order or income withholding order to the obligor at the obligor's last known post office address; or, in the alternative, a copy of the wage assignment order or income withholding order shall be served on the obligor in the same manner as a summons in a civil action on, before, or within two days after the date of service of the order on the employer. This requirement is not jurisdictional, but if the copy is not mailed or served as this subsection provides, or if any irregularity appears with respect to the mailing or service, the superior court, in its discretion, may quash the wage assignment order or income withholding order, upon motion of the obligor promptly made and supported by an affidavit showing that the obligor has suffered substantial injury due to the failure to mail or serve the copy.