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Simon Bridges told RNZ's Morning Report programme today the party is determined to crack down on gangs.
It's a value judgement, he said, and 92% of patched gang members have received a main benefit, he said.
Mr Bridges could not say how many children would be affected by blocking gang members from benefits.
"That's not the intention of the policy to get at the families, the intention is to get at the gang member," he said.
"There is a view out there ... a trendy sort of view put forward by people that gangs are about whānau and community, I reject that."
He said most patched gang members have received a benefit for an average of nine years.
"You've got a situation where the patched gang member can stump up and say you know what, actually that Harley Davidson it was paid for in this way, because I was a tradie for several years and this is how I made the money.
"If they can't do it, the truth is there's a reason why they can't do that, and that's because it's from ill-gotten gains."
Three-quarters of patched gang members are Māori.
Mr Bridges said Māori are also disproportionately victims by crime.
Black Power spokesperson Eugene Ryder said punishing families won't help anyone.
"I think [Simon Bridges is] talking to a part of society who have no idea about living in a low socio-economic areas. What he's doing is targeting people who are already on the cusp of society."
Taking away a source of income from people will encourage them to commit crime, he said.
"What he's trying to do is use the same rhetoric that is used every election which is how hard we are going to smash the gangs and who's got the biggest hammer.
"What he hasn't done is address the reason people are in gangs - because of the poverty that they live in."
A lot of people make money from illegal means, not just gang members, Mr Ryder said.
"There's an assumption that every gang member's a criminal and every criminal's a gang member, now that's just not true."
The policy is a presumption of guilt, he said.