The order, sent widely to civil society groups earlier this month, said all NGOs should refrain from "unauthorised activities with immediate effect".
"It has been revealed that certain Non Governmental Organisations conduct press conferences, workshops, training for journalists, and dissemination of press releases which is beyond their mandate," said the letter.
A group of 30 private charities and other organisations on Wednesday announced an alliance -- called the Civil Society Collective to Protect Civil Society Space -- to resist the restrictions.
"This demonstrates the lack of democracy in Sri Lanka," lawyer J.
C. Weliamuna, who runs the local chapter of anti-corruption group Transparency International, told AFP.
Authorities have often accused foreign and local charities of supporting dissidents and introduced tougher regulations to control them in 2010, a year after troops crushed Tamil rebels and ended decades of ethnic war
Weliamuna said his organisation would continue its