[GreyZephyr]

You don't need to even use the ACC, people for get that the 2005 counter-terrorism act[0][1] has provision for preventative detention without charge, and notably, made it a criminal act to tell anyone that you had been detained. Combined with a rather broad definition on what was terrorism and the ability of police to request information, documents and emails, this act seems to cover all of the functional aspects of the National security letters with even less oversight.

[0]http://www.ag.gov.au/NationalSecurity/Counterterrorismlaw/Pa... [1]https://en.wikipedia.org/wiki/Anti-Terrorism_Act_2005