Regulation (EC) No 715/2009 of the European Parliament and of the CouncilShow full title

9. Transmission system operators shall publish at least annually, by a predetermined deadline, all planned maintenance periods that might affect network users' rights from transport contracts and corresponding operational information with adequate advance notice. This shall include publishing on a prompt and non-discriminatory basis any changes to planned maintenance periods and notification of unplanned maintenance, as soon as that information becomes available to the transmission system operator. During maintenance periods, transmission system operators shall publish regularly updated information on the details of and expected duration and effect of the maintenance. U.K.