N.C. Gen. Stat. § 147-86.23
A State agency shall charge interest at the rate established pursuant to G.S. 105-241.21 on a past-due account receivable from the date the account receivable was due until it is paid. A State agency shall add to a past-due account receivable a late payment penalty of no more than ten percent (10%) of the account receivable. A State agency may waive a late-payment penalty for good cause shown. If another statute requires the payment of interest or a penalty on a past-due account receivable, this section does not apply to that past-due account receivable. This section does not apply to money owed to the University of North Carolina Health Care System or to East Carolina University's Division of Health Sciences for health care services, to the North Carolina Turnpike Authority for money owed to the Authority for tolls, or to the North Carolina State Health Plan for past-due account receivables related to premiums and claims payments.
N.C. Gen. Stat. § 147-86.23