Residential Customers and Residential Cooperatives. Each gas, electric, gas and electric, or telephone company using late payment charge provisions, policies, or practices for residential customers and residential cooperatives, may be authorized to apply to bills not paid within 20 days after the date of rendition up to 1-1/2 percent of the net bill, and at the end of the first nominal billing interval after that, an additional charge to be made equal to 1-1/2 percent of any portion of the original amount which remains unpaid at the time, and at the end of the second nominal billing interval, an additional charge to be made equal to 2 percent of any portion of the original amount which remains unpaid at the time. The total of the charges should not exceed 5 percent of the original unpaid amount. For residential customers and residential cooperatives, each gas, electric, gas and electric, or telephone company utilizing late payment provisions, policies, or practices authorized by this Commission shall apply the late payment charges to any bill or part of a bill not paid within 20 days calculated upon the net total cost less applicable taxes and, when applicable, the environmental surcharge. All Other Classes of Customers. Each gas, electric, gas and electric, or telephone company using late payment charge provisions, policies, or practices for all other classes of customers not provided for in §A of this regulation, may be authorized to apply to bills not paid within 15 days after the date of rendition up to 1-1/2 percent of the net bill, and at the end of the first nominal billing interval after that, an additional charge to be made equal to 1-1/2 percent of any portion of the original amount which remains unpaid at that time, and at the end of the second nominal billing interval, an additional charge to be made equal to 2 percent of any portion of the original amount which remains unpaid at the time. The total of these charges may not exceed 5 percent. For all other classes of customers not provided for in §A of this regulation, each gas, electric, gas and electric, or telephone company utilizing late payment provisions, policies, or practices authorized by this Commission shall apply the late payment charge to any bill or part of a bill not paid within 15 days calculated upon the net total cost less applicable taxes and, if applicable, the environmental surcharge. “Late payment charge” means an additional charge, over the net total cost of utility service provided, which is applied to any past-due bill under this regulation. Bill Extender Plan. A gas, electric, gas and electric, or telephone company using late payment provisions, policies, practices, and charges shall establish and offer to a residential customer a bill extender plan to assist the customer receiving monthly Social Security benefits, supplemental security income, disability payments, or other financial aid through government-sponsored assistance programs which constitutes the main source of income within the customer's household. The bill extender plan shall automatically extend a bill due date so that late payment charges are not incurred until: Thirty days after the date of bill rendition; A reasonable time following receipt of benefits or financial aid, as described in §D(1) of this regulation, by an eligible customer; or As provided in the utility's tariff. A utility customer shall request participation in the plan and provide adequate proof of eligibility.