"Coal is adding more and more carbon dioxide into the atmosphere and we are running into serious climate problems now," he said.
"Some people are taking it (carbon reduction) seriously and Fonterra does not seem to be doing so yet," he told the Herald.
Fonterra's 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 Maui gas - 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," he told the Herald.
Spurway said their had been a 16 per cent reduction in Fonterra's energy intensity - equivalent to 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.