A group of demonstrators protesting against Fonterra's use of coal descended on the company's Christchurch offices on Thursday.
The demonstrators, from Extinction Rebellion Ōtautahi, called Fonterra's ongoing use of coal "irresponsible".
The demonstration came after Bathurst Coal applied to expand the Canterbury Coal Mine, which sends a majority of its coal to Fonterra.
"The proposed expansion of the Canterbury Coal Mine has everything to do with Fonterra's addiction to coal," said Selina Clare, a spokesperson for Extinction Rebellion Ōtautahi.
"They are burning coal to dry out milk. Why are we seeing these irresponsible decisions in the middle of a climate crisis?"
Clare said the co-op needed to be accountable to the public for their use of coal.
Last year, Fonterra announced it would be slowly transitioning away from coal, putting a stop to installing any new coal boilers or increasing capacity to burn coal.
But Extinction Rebellion says despite the company's pledge "the proposed expansion of the Canterbury Coal Mine suggests this will not happen any time soon".
Michael Apathy, from Extinction Rebellion said as the coal mine's primary customer, Fonterra needed to be held responsible for the effect coal is having on the environment.
In announcing its intentions to use less coal last year, Fonterra said getting out of coal "is not as easy as flicking a switch" and required a staged approach.
The company is aiming to reduce emissions by 30 percent across all its operations by 2030 and achieve net-zero by 2050.
A spokesperson for Fonterra told Newshub the company was "making real progress" on changes to its carbon footprint and climate change.
"Last year we made the commitment not to install any new boilers or increase capacity to burn coal. We have also converted the boiler at our Brightwater site to co-fire on wood biomass and are carrying out work at our Stirling Site to move away from coal. The move to wood pellets at our Te Awamutu site this season will save us more than 84,000 tonnes of carbon emissions the same as taking 32,000 cars off the road.
"We do not have any plans to increase our coal consumption, which we use to fuel our boilers to generate process heat to make our dairy products."
The spokesperson said the company did not comment on the commercial operations of other businesses and respected the right of all New Zealanders to protest peacefully.
Organisers told Newshub around 40 people attended the protest and said Extinction Rebellion may stage more protests depending on Fonterra's response.