The Court of Appeal has ruled the trial of 21 Red Devils motorcycle gang members from Nelson can go ahead, despite serious police misconduct.
The High Court had stayed a total of 151 charges because police faked the arrest of an undercover officer to build up his credibility.
But the Court of Appeal says the misconduct which included including faking a search warrant and having the undercover police officer charged and appear in court under a false name, was very serious.
However, Tuesday's ruling says there was only a weak link between the misconduct and the intended trial, and not to proceed with a trial would be an abuse of process.
The accused face offences including taking part in an organised criminal group, supplying methamphetamine and conspiring to cause grievous bodily harm.
A lawyer for three of those charged, Tony Bamford, says they are considering taking the case to the Supreme Court after that decision was reversed by the Court of Appeal.
Mr Bamford says they may also challenge whether some evidence in the case should be ruled inadmissable due to police misconduct.
The Police Association says it will now be more difficult for police to inflitrate gangs and criminal organisations.
Association president Greg O'Connor says it does raise some new concerns. "Police cannot and should not operate outside the law. The law has been clarified and it will make it more difficult to infiltrate criminal gangs."
Mr O'Connor says gang members and organised criminals will be happy with the comments accompanying the ruling.