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.

But he said the company, owned by Mighty River Power which the Government plans to list on the sharemarket after the election, now seemed to be taking "a hard line".

"They did make a commitment when Folole Muliaga died that they would work alongside budget services. That seems to have well and truly lapsed, certainly with my organisation," he said.

Lynfield couple Allison and Peter Jones, who have been with Mercury ever since they were married 34 years ago, said they were "wild" when they received a letter last Friday threatening to put them on Glo-Bug after missing one payment because their bill was lost in the post.

Mrs Jones, who pays the bills online, said she had never missed a bill before.

"I always pay the bill," she said.

"They are not the cheapest power company but we have been loyal to them all these years and this is just a slap in the face."

The letter tells people the company "will exercise our right to move you to our Glo-Bug prepaid service 30 days after the date of this letter" unless they pay their bills within seven days.

Glo-Bug charges work out at almost the same for an average Auckland customer with a power bill of around $190 a month, except that Glo-Bug customers do not get the 10 per cent early-payment discount. They also pay a 60c fee every time they top up their account.

Mercury general manager James Munro said the company started sending the letters out with first reminder notices last month because the Electricity and Gas Complaints Commission had ruled that it must give at least 30 days notice before moving customers on to Glo-Bug compulsorily.

But he now saw that the letter's wording "could be improved".