Direct Animal Action went into the chicken shed through an unlocked door at a farm near Helensville and shot footage of birds with large open wounds and some lying on their backs unable to move.
The group is calling for Tegel to be prosecuted over its treatment of the birds at the farm but the poultry giant rejects accusations that it does not look after its animals.
RNZ was invited by Tegel to the farm where the footage was shot. RNZ did not see chickens with open wounds or that look hurt or deformed as they were in the video.
Tegel chief executive Phil Hand said the wounds in the footage shot by Direct Animal Action were interesting.
"[We] wouldn't normally see that and I can't comment on what would have happened that day - I wasn't in the shed.
"But as with any animal, not all of them will be perfectly healthy throughout their entire life, no different to humans."
Mr Hand said the farmer goes through the shed multiple times a day to cull any birds that are unwell, as required by the code of welfare.
But he said when the video was shot, the farmer was not there.
"The birds weren't due for a walk-through for quite a few hours and so there would have been some birds who ... needed some assistance from the farmer or who needed to be culled and that would have happened when the farmer came through."
It appeared the activists had moved through the shed and disturbed the chickens, Mr Hand said.
"It certainly looked from the video we saw that the birds were in an agitated state and that was because they were surprised.
"In doing what they did, they endangered our birds and put them at risk.
He said he was concerned about how the birds appeared in the film.
Direct Animal Action spokesperson Deirdre Sims said Tegel should be disappointed in themselves.
"We absolutely did not stir up the birds. We just literally filmed what was happening in front of us.
"I think that's just typical that Tegel would say something like that to try and make us look bad because they're on the back foot."
Mr Hand said the Ministry for Primary Industries investigated the Tegel farm on Friday and told the farmer there were no issues.
If there were concerns MPI should have raised them.
But MPI said it was still reviewing footage and could not comment while the farm was being investigated.
Application for mega chicken farm stalled for odour modelling
Tegel has also been asked by the Northland Regional Council and the Kaipara District Council to provide information on odour modelling, delaying its plans to build the country's biggest chicken farm.
Tegel applied for resource consents to raise nine million birds a year, partly in barns, 12 kilometres south of Dargaville, near the Northern Wairoa River.
Mr Hand said it could take a few months to get data on the technology they wanted to use to reduce odour because it was in Europe.
The request from the two local bodies was a surprise because they had not previously raised the issue.
Locals had come to Tegel with concerns about dust and smell but there had also been support for the farm.
"We don't want to have a farm up there that is causing a nuisance or an offence to the neighbours."
This article was first published on RNZ.