A firearms dealer is questioning police for raiding the homes of licensed firearms owners and confiscating semi-automatic weapons.
Since the 15 March mosque attacks in Christchurch, the government has banned semi-automatic guns.
Six gun owners have complained to the Independent Police Conduct Authority about searches of their properties.
New Zealand Ammunition co-owner Paul Clark said he had talked to gun owners who had experienced armed police turning up at their homes.
None of those who had been raided ended up being prosecuted, Mr Clark said.
"If it's that bad and you have to come in with up to half a dozen armed police - or more in some cases - if it's that serious, why aren't the people in court for their first appearance?" Mr Clark said.
He said he hoped the police raids have now stopped.
Police said since the mosque shootings, they had been tipped off to concerning behaviour, requiring visits to both licensed and unlicensed gun owners.
Some visits showed there was no risk to the public, while others could require further interventions, such as seizing guns or arresting people.
"The police presence during these visits is based on a risk assessment," a police spokesperson said.
"Police must respond in a manner that protects officers and the public as enquiries are undertaken.
"Many of these reports are from members of the public who are being vigilant, as we have asked them to be, and have rightly passed their concerns on to police."
Police will hold firearm collection events across New Zealand until a gun amnesty period ends on 20 December.