A power outage in June 2008 left downtown Washington without electricity for hours. The blackout snarled morning rush hour and forced a number of offices to close, affecting as many as 12,000 customers of the Potomac Electric Power Co., or Pepco.

The District of Columbia Public Service Com­mission launched an investigation, only to find itself entangled in a discovery dispute over whether Pepco can claim the right to withhold certain infrastructure information in the name of national security. Now pending before the D.C. Court of Appeals, the case has pitted the commission against the Office of People’s Counsel (OPC), the city agency tasked with representing utility consumers in these investigations.