N.C. Gen. Stat. § 54-57
A borrower may repay his loan by installments of such frequency and amounts as may be agreed upon: Provided, that not less than one percent (1%) of the original amount of the mortgage shall be paid upon the principal thereof annually, and commencing not later than the sixth year succeeding the year in which the loan was made the borrower may pay a larger installment upon the principal, or the whole of it, at any interest date, such payments to be in amounts equal to additions of one or more principal amortization payments. Such payment may be made in cash, or by tendering at par bonds of the association. For failure to pay the interest or any installment required by the terms of the loan, the borrower may be fined as the bylaws may prescribe. But the borrower shall never be required to pay more than the specified installment, nor to pay the principal before it is due except as prescribed herein for partial repayment on account of depreciation and for foreclosure by the association. The borrower may on 60 days' notice repay the association his total indebtedness, or, without such notice, upon payment of 60 days' interest upon the principal unpaid. The borrower shall be entitled to a receipt for all installments as paid, and where the repayment is complete to a satisfaction of his note and mortgage.
N.C. Gen. Stat. § 54-57