The discovery of poisonous spiders in bags of Mexican grapes has drawn a warning that lax biosecurity could put the horticultural industry at risk.
The black widow spiders don't pose a serious danger to humans and aren't a threat to the industry.
But Labour says if they can get in, so can serious pests such as the glassy winged sharpshooter and others that could wreak havoc.
"The fact is these spiders entered the country through the 'usual channels' which may or may not have included fumigation," said Labour's Damien O'Connor.
"That's hardly a robust system ... there might be more sniffer dogs at airports to check baggage, but there's clearly insufficient scrutiny of commercial and container imports."
Primary Industries Minister Nathan Guy is defending the system and says 175,000 items cross the border every day.
"From time to time, because of the volume, there is unfortunately a breach," he said on Radio New Zealand today.
Mr Guy says all grapes on the way from Mexico will be fumigated or destroyed.
To date, 10 spiders have been found in grapes at several locations around the country.
All grapes imported from Mexico have been pulled from sale.
The ministry's surveillance manager Brendan Gould says it's likely some grapes from the affected shipments will have already been sold.
People who have recently bought table grapes should check them carefully for spiders. If they do find one, the grapes and spider should be bagged and sealed and MPI should be contacted.
"We take this matter very seriously and we are investigating how this breach has occurred and taking measures to tighten up the system," Mr Gould said.