A federal appeals court is asking the Obama administration to explain why the government should be allowed to keep secret its plan to shutter mobile phone service during "critical emergencies."

The Department of Homeland Security came up with the plan—known as Standing Operating Procedure 303—after cellular phones were used to detonate explosives targeting a London public transportation system.

SOP 303 is a powerful tool in the digital age, and it spells out a "unified voluntary process for the orderly shut-down and restoration of wireless services during critical emergencies such as the threat of radio-activated improvised explosive devices."

The US Court of Appeals for the District of Columbia Circuit in February sided (PDF) with the government and ruled that the policy did not need to be disclosed under a Freedom of Information Act request from the Electronic Privacy Information Center. The court agreed with the government's citation of a FOIA exemption that precludes disclosure if doing so "could reasonably be expected to endanger the life or physical safety of any individual."

EPIC asked the court to revisit its ruling, arguing that the decision, "if left in place, would create an untethered 'national security' exemption'" in FOIA law. On Friday, the court ordered (PDF) the government to respond—a move that suggests the appellate court might rehear the case.

EPIC originally asked for the document in 2011 in the wake of the shut down of mobile phone service in the San Francisco Bay Area subway system during a protest. The government withheld the information, EPIC sued and won, but the government then appealed and prevailed.

In its petition for rehearing, EPIC argued that the appellate court's decision "created a catch-all provision that would allow federal agencies to routinely withhold records subject to disclosure where the agency merely asserts a speculative security risk."

Under the direction of the so-called National Security Telecommunications Advisory Committee, SOP 303 allows for the shutting down of wireless networks "within a localized area, such as a tunnel or bridge, and within an entire metropolitan area."

There have been no publicly disclosed instances when SOP 303 has been invoked, but the telecoms have agreed to shutter service when SOP 303 is invoked.

Local governments, however, have the power to shutter wireless service regardless of SOP 303.

The last known time mobile phone service was cut by a government agency was the San Francisco example from 2011. That's when the Bay Area Rapid Transit System took heat for disabling service to quell a protest in four downtown San Francisco stations. The three-hour outage was done after BART cut service without the assistance of the telcos.

In the aftermath, BART produced a new policy that said service could only be cut off when "there is strong evidence of imminent unlawful activity that threatens the safety of district passengers, employees, and other members of the public."