Bills not paid by the twentieth day of the month (or first workday thereafter) shall be subject to a late payment fee. This fee shall be calculated at one percent per month of the outstanding balance, and a minimum fee of $1.00 per service class (a bill with water, sewer, and garbage would be three service classes) for each month or portion thereof past due, whichever is greater. [Ord. 91-22 §2, 1991; Ord. 87-32-O §2, 1987; Ord. 85-21-O §1, 1985. Formerly §13.01.155].