except that, with respect to the disposable earnings of any individual for any workweek, the fifty percent specified in subdivision a must be deemed to be fifty-five percent and the sixty percent specified in subdivision b must be deemed to be sixty-five percent, if and to the extent that the earnings are subject to garnishment to enforce a support order with respect to a period which is prior to the twelve-week period which ends with the beginning of such workweek.
N.D.C.C. § 32-09.1-03