This excerpt taken from the PCG 10-K filed Feb 18, 2005.
6.2. Transmission Service.
6.2.1 Compliance with Tariffs. Participating TOs shall allow access to their transmission facilities (including any that are not for the time being under the ISO's Operational Control) only on the terms of the ISO Tariff and the TO Tariff.
6.2.2 Release of Scheduling Rights. When required by the ISO, a Participating TO shall release all of its scheduling rights over the transmission lines and associated facilities that are part of the ISO Controlled Grid to the extent such rights are established through Existing Contracts among or between Participating TOs, as provided in the ISO Tariff.