N.J. Stat. § 2A:50-43: Foreclosure for unpaid installment of principal authorized

Whenever, under the terms of a mortgage it is provided that there shall be paid on account of the principal sum secured thereby any payment on account thereof, due at a time or times therein specified, the holder of the mortgage may, whenever the owner of the mortgaged premises defaults in making any such payment on account of the principal sum, at the time when the same has become due, or within such period of grace as is designated in the mortgage or the evidence of debt secured thereby, elect to foreclose the mortgage only to the extent that there is due and unpaid thereunder any payment required to be made on account of the principal, either by the terms of the mortgage or the evidence of debt secured thereby.

L.1951 (1st SS), c.344.