The Court of Appeal has reserved its decision on whether those arrested following nationwide police raids in 2007 should be tried by a jury or a judge sitting alone.
Some 18 people face a variety of charges under the Arms Act as a result of the raids and five others are charged with participating in a criminal group.
At the High Court in December last year, Justice Winkelmann ruled their trial should take place before a judge alone.
Lawyers for the accused told the Court of Appeal on Thursday the right to trial by jury is so entrenched in the New Zealand legal system that the highest possible standards must be applied before it is removed.
However, lawyers for the Crown said Justice Winkelmann was correct to decide that the trial should take place before a judge alone and she had considered all the relevant factors in reaching that decision.
The trial is due to take place in Auckland in May.