A group protesting Fonterra's use of coal in its factories is promising not to back down.

Auckland Coal Action group drew attention at Fieldays on the weekend.

It handed out false flyers advertising Fonterra's imaginary switch from coal to wood chips, as fuel for its milk powder dryers.

Spokesperson Jeanette Fitzsimons said if New Zealand wants to do its fair share to combat climate change, Fonterra has got to get off coal.

She said it's one of New Zealand's biggest contributors to climate change-causing emissions, using more than half a million tonnes of coal every year.

"It's the biggest user of coal, except for the steel mill which doesn't have other options, and Huntly power station which is sort of in the process of closing down."

The leaflets were just the start of the group's campaign.

"We're going to be keeping the pressure on in a number of ways, until eventually they start converting their boilers and stop their coal use."