Facebook among tech firms battling gag orders over government surveillance

US government prevents companies from revealing many user data requests - a practice which firms and civil liberties activists call unconstitutional

Tech companies including Facebook, Twitter and Microsoft are fighting gag orders from US courts preventing them from talking about government surveillance of their users, arguing it has a chilling effect on free speech.

Facebook, Twitter and Microsoft all have policies to notify users of government requests for account information unless they are prohibited by law from doing so in exceptional circumstances such as life-threatening emergencies, child sexual exploitation and terrorism.