Here are a couple of quick reactions.
A statement from the Aliran exco:
RPK’s detention is unjust as it denies him his democratic right to defend himself. He should have been charged in open court in relation to the earlier charges made against him under the Sedition Act. By resorting to the ISA, his innocence can no longer be proven. This is indeed undemocratic, unjust and un-Islamic. Full statement: Release Raja Petra and retract show-cause letters
Aliran member Toh Kin Woon has also come out strongly:
It is blatantly obvious that the state is now resorting to the use of dictatorial and draconian measures to intimidate all those who wish to tell and reveal the truths. Even those who merely do their job honestly as journalists and the newspapers that they work for are not spared. It is increasingly obvious, too, that the present Federal Government is not prepared to allow the space for freedom of speech, including the freedom of the press. Full statement here.