Fam. Code, § 5238

(a) Where an assignment order or assignment orders include both current support and payments towards the liquidation of arrearages, priority shall be given first to the current child support obligation, then the current spousal support obligation, and thereafter to the liquidation of child and then spousal support arrearages.

(b) Where there are multiple assignment orders for the same employee, the employer shall prorate the withheld payments as follows:

(1) If the obligor has more than one assignment for support, the employer shall add together the amount of support due for each assignment.

(2) If 50 percent of the obligor’s net disposable earnings will not pay in full all of the assignments for support, the employer shall prorate it first among all of the current support assignments in the same proportion that each assignment bears to the total current support owed.

(3) The employer shall apply any remainder to the assignments for arrearage support in the same proportion that each assignment bears to the total arrearage owed.