52 Pa. Code § 53.10
Each tariff revision or supplement filed with the Commission shall be accompanied by a letter of transmittal, in duplicate if receipt is desired, prepared on paper 8 1/2 by 11 inches in size. Specific reference shall be made to the tariff revision, or supplement being filed, its effective date, and such supporting data as may be required by § § 53.51-53.53 (relating to information furnished with the filing of rate changes), unless such supporting data have been previously filed. The original will be retained by the Commission. The duplicate, if any, when accompanied by postage sufficient to cover return mailing, will be stamped and returned to the public utility to evidence receipt of the tariff matters filed. When a number of tariffs, revisions or supplements pertaining to one kind of public utility service are filed simultaneously, they may be included in one transmittal letter. Separate letters shall be used for tariffs, revisions or supplements filed for different kinds of public utility service. If the tariff filed is a joint one, the letter of transmittal shall include a statement to the effect that it is concurred in by all participants, under appropriate authorization on file with the Commission or attached to the letter.
52 Pa. Code § 53.10