An online video reportedly shot inside a Tegel chicken barn in Helensville has been described as a 'shock and horror'.
The footage was filmed by the animal welfare group Direct Animal Action at a plant near Helensville.
The Ministry for Primary Industries (MPI) visited the Helensville farm on Friday and is reviewing footage of the apparently dead and deformed chickens.
Warning: The content in this video may be distressing for some people.
The group is calling for poultry giant Tegel to be prosecuted over its treatment of chickens at the farm.
However, Tegel has rejected accusations that it does not look after its chickens, saying the video was selective and did not accurately reflect the farm's practices.
"With any population of farmed animals, there will be a small number that don't develop as they should and are removed," Tegel said in a written statement.
It said the farm passed its independent welfare audit conducted by AsureQuality in March.
The company said it checked its sheds daily and removed birds that were dead or abnormal.
The Ministry for Primary Industries investigated the farm on Friday and did not raise any complaints, the company said.
MPI said it was still reviewing the footage and could not comment while the farm was being investigated.
Direct Animal Action spokesperson Deidre Sims said during two separate visits she saw many maltreated birds and wanted Tegel prosecuted for failing to meet welfare standards.
"Chickens with large open wounds, putrid rotting dead bodies, chickens laying on their backs unable to get up to access food and water," Ms Sims said.
"From our point of view if MPI don't prosecute over that, we will be disappointed," she said.
The public is often left in the dark about animal welfare, she said.
"We just took a look behind closed doors of Tegel's farm and exposed some pretty graphic suffering that we thought was pretty shocking," she said.
The group managed to walk in through an unlocked door to film during two visits in the last month.
Ms Sims said maltreatment of this kind comes down to "sheer laziness".
"There's a code of welfare for meat chickens which says farmers must go through their farms on a daily basis and remove dead bodies or humanely destroy chickens that are suffering," Ms Sims said.
"From what we witnessed, this farm was not doing that."
The footage was a black mark against Tegel's application for a mega-farm in Northland, Ms Sims said.
Last week, the company suspended its application to raise 9 million chickens a year on land south of Dargaville, saying it wished to address local government concerns.
SPCA spokesperson Arnja Dale said the footage was not necessarily indicative of wider industry issues but it did show that it was highly unlikely the sheds had been checked daily.
"What we saw in that footage is not how anyone would want their meat farmed.
"That level of suffering is unacceptable and we are pleased the ministry is investigating them," she said.
Tegel does not receive SPCA's blue tick of farming welfare approval but Dr Dale could not explain why, due to a confidentiality agreement.
Kaipara community voices opposition
The local Kaipara community has widely opposed the development of the farm.
Artist David Sarich, who's painted protest signs for Kaipara objectors, said the birds in the video look deformed and many are injured.
As a group, the objectors could only oppose Tegel farm issues under the Resource Management Act requirements, Mr Sarich said.
"But for me personally, the animal welfare, that's a shock and a horror and we should not be allowing this in our country."