California regulators will require 72 hours of backup power at cell towers in emergency situations, including electricity shutoffs during fire seasons.
The California Public Utilities Commission voted unanimously Thursday to adopt the measure.
Last fire season, more than a million people lost service during planned blackouts.
The resulting public outcry prompted legislators and advocates to push for measures that would require backup power in vulnerable areas.
AT&T said after the vote that it is focused on ensuring that backup power is available routinely during public safety power shut-offs.