A charge of two percent (2%) per month shall be paid on the opening monthly balance on accounts remaining unpaid over thirty (30) days after the billing date. [CGD 79-138, 45 FR 13078, Feb. 28, 1980. Redesignated at 61 FR 32655, June 25, 1996, and further redesignated by USCG-1998-3976, 63 FR 35139, June 29, 1998]