Gangs have made multiple attempts to infiltrate the police and efforts to pre-screen recruits need to be stepped up, the Police Association says.
The union's president, Chris Cahill, told Nine to Noon gangs had spread wider, their member numbers had increased and they were working closer together.
"The gangs are certainly increasing their presence and they've got the upper hand in some areas. That's why we need more resources in some of the provincial centres to tackle the gangs increasing their profile there."
A Headhunter gang member had corrupted an Auckland police officer, who ended up dealing methamphetamine for them a couple of years ago in Waitakere, he said. He also knew of instances where gang members had tried to join the police force.
"We just believe if [infiltration] was to happen, and it was to happen on a co-ordinated approach, it would be seriously damaging to not only the reputation of police but to law and order right across New Zealand."
Stringent security measures and robust systems were needed, especially because the police were recruiting 220 officers each year, he said.
Mr Cahill said other organisations tackling corruption across the country also needed adequate resources.
"The Department of Internal Affairs looks into a number of small money remitters that operate throughout New Zealand that are, to a large degree, unpoliced due to low resourcing.
"That's where a lot of the money laundering in New Zealand takes place, so we believe they also need to be resourced. It's not just about police, it's other government departments as well."
The Police Association, which released its policy manifesto yesterday, said other changes needed included greater restrictions on the sale of firearms, more use of mobile technology to deal with family violence, and harsher penalties for drivers who failed to stop for police.