A ban is already in place preventing media from recording or filming the hearing at Auckland District Court on the grounds that there are serious security issues.
Nineteen of the 20 arrested face charges under the Arms Act, with one also facing a cannabis charge. The last person will have his case heard in Tauranga in November.
The group was arrested after police raids last October which centred on the Bay of Plenty settlement of Ruatoki.
Several of those arrested in the raids are Maori, including prominent Tuhoe activist Tame Iti.
Police alleged he was running military-styled training camps in the Urewera Ranges. However, the Solicitor-General ruled against the application from police to charge him and others under the Terrorism Suppression Act.
At this week's hearing, the Crown will seek to prove a "prima facie" case against each of the accused to show they have a case to answer before a jury. Defendants committed from these hearings are expected to face jury trials in mid to late-2009.
The hearing is expected to run until September 11, followed by a recess, and the court will sit again on September 22. Defendants have said it may run as long as October 3 as many are expected to give evidence in Maori.
Iti's lawyer, Annette Sykes, expects the morning to be taken up by defence lawyers' applications for blanket suppression orders.
Activists who marched in protest at the charges in Auckland and Wellington over the weekend said they expected further charges may yet be laid against some of the accused.
Peter Williams QC is acting for the Tuhoe iwi which is aggrieved over the raids and is seeking a settlement from the police, preferably without recourse to the courts.
Tuhoe spokesman Tamati Kruger said that most of all the Tuhoe people wanted an end to what had been a very long, difficult process.
