N.C. Gen. Stat. § 58-74-35: When additional security required.

If, from any cause, the property mortgaged in lieu of a bond becomes of less value than the amount of the bond in lieu of which the mortgage is given, and it so appears upon affidavit of any person having any interest in the matter as a security for which the mortgage was given, it is the duty of the mortgagor to give additional security by a deposit of money, or the execution of a mortgage on more property, or justify as required in cases where bond or undertaking is given. (1874-5, c. 103, s. 5; Code, s. 119; Rev., s. 271; C.S., s. 352.)