Anti-coal campaigners say the dairy giant Fonterra should cut back on the amount of coal it uses in its factories.
The comments come after electricity company Genesis Energy announced last week that it would close its last two coal-fired boilers at the Huntly Power Station.
But the call for Fonterra to also switch away from coal has been criticised as bad timing when the dairy industry is struggling to get by.
Coal produces far more greenhouse gases than other fuels to produce the same amount of energy.
As a result, climate change campaigners are delighted to see an end to coal burning by Genesis Energy.
That company announced last week that it would phase out coal burning at its Huntly power station by 2018.
Former Green Party co-leader Jeanette Fitzsimons now campaigns for Coal Action Network Aotearoa and said the focus of her campaign must now go onto Fonterra.
"With the Huntly power station closing and the steel mill having no other options at the moment other than using coal, the biggest coal user in New Zealand now and therefore the biggest climate changer is Fonterra," she said.
Fonterra needs vast amounts of energy to convert liquid milk into milk solids.
It actually owns its own coal mine and also buys coal from elsewhere.
Jeanette Fitzsimons said its record was actually getting worse.
"It has been growing its coal use very fast and it intends to continue growing its coal use fast," she said.
"That is unacceptable in a climate changing world and it does have an option. It could use waste wood forestry residues, there are contractors who would supply it and it would run boilers perfectly well."
Fonterra was not available for an interview on this subject.
But the company did put out a statement, saying it was constantly trying to improve its environmental record by improving its energy intensity: in other words, by making more milk powder for less energy.
"Despite expansion across our manufacturing plants to keep pace with rising New Zealand milk volumes, we have delivered year-on-year improvement in energy intensity resulting in a 16 percent reduction in energy intensity since 2003," it said.
"Investigation of options for cleaner burning, more efficient energy sources form a key part of our energy strategy, and include our recent trials of biofuels from Miscanthus and the assessment of technologies that allow us to co-fire biomass in a number of our newer plants.
"Coal is used by a third of Fonterra's manufacturing sites - the majority in the South Island where we do not have the option of using natural gas."
Meanwhile, a professor of agribusiness at Massey University is defending Fonterra's record.
Hamish Gow thinks now is not the time for a wholesale switch in energy usage by Fonterra.
"Just like any other household or business you have got to work within your means," he said.
"So making a new investment in a different type of energy source while you are facing the lowest prices in 15 years is just a totally unrealistic expectation," he said.
"It is nice to argue for but in reality it would never make business sense for Fonterra to change their energy source at the moment."
Jeanette Fitzsimons said her call was for old boilers run by Fonterra to be modified gradually but all new boilers should be run on wood waste.