A fierce backlash from customers has forced Mercury Energy to review the wording of a letter it has sent to late-paying customers threatening to shift them on to pre-paid meters.
Customers who have never been late paying a power bill before have been sent the letter if they did not pay their latest bill by the deadline required for an early-payment discount - even if they still paid before the final due date.
Some say they will switch to other power companies in protest.
Mangere Budgeting Service chief executive Darryl Evans said his service had been "inundated" with people who received the letters.
Mr Evans welcomed the Glo-Bug pre-pay system when Mercury introduced it after it cut off power to Mangere resident Folole Muliaga, knocking out the oxygen therapy machine she depended on to stay alive. The Glo-Bug meter turns orange and then red to warn people before their money runs out.