Executives from Facebook, Twitter and BlackBerry maker Research in Motion Ltd. are meeting the British government and police to discuss how to prevent social networks being used to plot violence.
The government has expressed concern about the way social media and BlackBerry's instant messaging were used during this month's riots across England.
Civil libertarians reacted with alarm to suggestions the services could be shut down in times of crisis.
A Home Office spokeswoman said there was "no suggestion" the sites would be closed down.
But she says Thursday's meeting will discuss "whether and how we should be able to stop people communicating via these websites and services when we know they are plotting violence, disorder and criminality."