Passengers travelling to the US could have their electronic devices seized by airport security if the equipment does not turn on.
The move comes as part of a security clampdown at airports with direct flights to the US after American officials last week warned of a "credible" terrorist threat.
The increased checks are featuring at UK airports, including Heathrow.
The new restriction means that any electronic device that has a flat battery may not be allowed on to the flight.
A statement from the Transportation Security Administration (TSA) said: "During the security examination, officers may also ask that owners power-up some devices, including cell phones.
"Powerless devices will not be permitted on board the aircraft. The traveller may also undergo additional screening."