Fonterra is proud of the energy-efficiency gains it has made over the past 12 years - but the giant dairy co-operative gets a black mark from Coal Action Network Aotearoa (Cana) for its "addiction" to coal.
Five Cana members - three grandmothers, a student and a farmer - chained themselves to a gate to prevent coal being delivered to Fonterra's Clandeboye dairy factory in South Canterbury.
"Fonterra is our second largest user of coal and this factory burns 180,000 tonnes of coal a year," said Cana's Jeanette Fitzsimons, former leader of the Green Pary.
"All of this ends up in our atmosphere, contributing to climate change. It's time for Fonterra to keep the coal in the hole and switch to woodchips instead.
"Fonterra's coal use is also propping up the mining industry - coalmines around the country are being reopened and extended because of Fonterra's addiction to coal."
Two dozen Cana members were said to be protesting at the site.
A Fonterra spokesperson said the co-operative was committed to reducing environmental impact of its operations through the use of new technologies and more efficient forms of energy.
"We measure our performance based on energy intensity per tonne of product, and set the standard within the New Zealand dairy sector based on this metric," the spokesperson said.
"Like the Coal Action Network, we are conscious of the impacts that all industries have on emissions and stand behind our commitment to reduce our footprint so that dairy can continue to play an important role in New Zealand's prosperity.
As a responsible corporate citizen, we too believe a transition away from coal will be the only sustainable future for dairy production."
The protest follows a similar demonstration outside Fonterra's head office in Auckland in December.
Fonterra uses the intense heat generated by coal and gas for a network of driers which take the water out of milk in order to turn it into milk powder.
Fonterra chief operating officer, global operations, Robert Spurway said three out of the co-op's 17 North Island plants still use coal.
The South Island plants, which don't have the benefit of pipeline gas, all use coal.
"We are New Zealand's largest business and conversion of milk into dairy product is an energy intensive business," he said.
"Our focus has traditionally been on making that as energy efficient as we possibly can."
Spurway said there had been a 16 per cent reduction in Fonterra's energy intensity - equivalent to the energy demand of Wellington - over the last 12 years.
"We are proud of that but we are actively looking at solutions to further reduce energy and to move away from coal," he said.
Fonterra said it buys only low sulphur coal and has installed emission control systems at most of its plants.