The collection of Fonterra farmers' milk and the co-op's operations will be prioritised under new restrictions to try and curb the spread of COVID-19.
On Monday, the Government announced a move to a level 3 alert, to be followed by level 4 in 48 hours.
All non-essential businesses must close, as well as bars, restaurants, cafes, gyms, cinemas, pools, museums, libraries, and playgrounds.
In announcing the new levels, Prime Minister Jacinda Arden said food suppliers were classified as an essential service.
"Those who are part of the food supply chain, who provide for our supermarkets, are part of our essential primary industry," said Ardern.
Fonterra CEO Miles Hurrell told Newshub that it had received advice from the Government that Fonterra is considered an essential service.
"As part of the food supply chain, the collection of Fonterra farmers' milk and our operations will be prioritised," said Hurrell.
He said Fonterra employees in the food supply chain, such as farmers, tanker drivers, manufacturing and distribution centre employees, were to keep working but follow the very strict guidance from the government to protect themselves and the community from COVID-19.
"The Government has shown a lot of trust in us to keep operating under a level 4 alert.
"This is a big responsibility. I sincerely thank all our people who will continue to keep dairy in production for everyone's health and nutrition during this difficult time."
All Fonterra staff who are able to work from home would do so.
The Fonterra owned Farm Source retail stores across New Zealand would be closing for the time being, however people would still be able to shop online, he said.