75 Pa. C.S. § 6145
If any jurisdiction permits or requires the licensing of fleets of vehicles in interstate or combined interstate and intrastate commerce and payment of registration fees, license taxes or other fixed fees on an apportionment basis commensurate with and determined by the miles traveled on and the use made of the jurisdiction's highways, as compared with the miles traveled on and the use made of another jurisdiction's highways or any other equitable basis of apportionment, and exempts vehicles registered in other jurisdictions under such apportionment basis from the requirements of full payment of its own registration, license or other fixed fees, then the secretary may, by agreement, adopt the exemption with respect to vehicles of such fleets, whether owned by residents or nonresidents of this Commonwealth and regardless of where based. The agreements, under such terms, conditions or restrictions as the secretary deems proper, may provide that owners of vehicles operated in interstate or combined interstate and intrastate commerce in this Commonwealth shall be permitted to pay registration, license or other fixed fees on an apportionment basis, commensurate with and determined by the miles traveled or the use made of the highways of this Commonwealth as compared with the use made of the highways of other jurisdictions or any other equitable basis of apportionment. No agreement shall authorize, or be construed as authorizing, any vehicle so registered to be operated in intrastate commerce in this Commonwealth unless the owner has been granted intrastate authority or rights by the Pennsylvania Public Utility Commission if such grant is otherwise required by law. The secretary may adopt and promulgate such rules and regulations as deemed necessary to effectuate and administer the provisions of this section, and the registration of fleet vehicles under this subchapter shall be subject to the rights, terms and conditions granted by or contained in any applicable agreement, arrangement or declaration made by the secretary.
75 Pa.C.S. § 6145