The cost of electricity in some of the country's poorest regions could be set to rise, according to a working paper released by the Electricity Authority.
It said transmission charges could rise by about 10 percent in Northland and the West Coast, and about five percent in Marlborough and parts of Auckland.
The authority is looking at updating the way charges are set in the light of recent investment of more than $2 billion in the national grid, particularly in the North Island.
It said the areas that benefit most from that investment should be charged accordingly.
Salvation Army social services secretary Pam Waugh said Northland and the West Coast were already particularly deprived areas, and any increases would hit those people hardest.
"We will see more people taking cuts on keeping their houses warm, which we see a lot of during the winter with the families that we work with," she said.
"So you'll see health issues coming up, you'll see limits on food being given to families because they've got to meet these costs."
Ms Waugh said when families could not afford heating, illnesses such as rheumatic fever tended to rise.
The paper has been released to the country's 28 local lines companies for discussion.