Any public utility which imposes penalties upon its customers for failure to pay bills promptly, or allows its customers discounts for prompt payment of bills, shall provide in its posted and filed tariffs a rule clearly setting forth the exact circumstances and conditions in which the penalties are imposed or discounts are allowed. The tariff shall also indicate clearly whether, if bills are paid by mail, the date of the postmark will be considered the date of payment.
52 Pa. Code § 53.84
This section cited in 52 Pa. Code § 56.223 (relating to repealers).