The order came from DHS Secretary Jeh Johnson, who confirmed he "directed TSA to implement enhanced security measures in the coming days at certain overseas airports with direct flights to the United States". According to Secretary Johnson's statement, the DHS is liaising with "foreign allies" and airlines, and "will work to ensure these necessary steps pose as few disruptions to travelers as possible".
The reinforced security checks reportedly come in response to an alleged terrorist threat, the details of which are unknown, as well as intelligence that suggests bombs involving cell phones and shoes are being made by terrorists in Yemen and Syria.
Thus far, overseas airport to officially comply with this new rule are London's Heathrow Airport and Manchester Airport, while British Airways passengers will also have their powerless electronics denied. According to the BBC, the UK, Germany, and France have said they will meet the requirement.