N.C. Gen. Stat. § 110-136.7: Multiple withholding.

When an obligor is subject to more than one withholding for child support, withholding for current child support shall have priority over past-due support. Where two or more orders for current support exist, each family shall receive a pro rata share of the total amount withheld based on the respective child support orders being enforced. (1985 (Reg. Sess., 1986), c. 949, s. 2.)