Embattled Mercury Energy now faces a new revolt - this time from the elderly - just as it apologises to 18,000 customers for threatening to move them on to pre-paid meters.

General manager James Munro, who is also retail general manager for parent company Mighty River Power, drew a storm of protest last week from long-time Mercury customers who received the threatening letter after missing the prompt-payment discount date for one power bill.

Now he also faces a Grey Power petition protesting against charges for paying power bills by cheque, credit card or over the counter.

The letter told customers who were late with one bill in the past month that unless they paid their bill within seven days, Mercury would "exercise our right to move you to our Glo-Bug pre-paid service 30 days after the date of this letter subject to Glo-Bug being available in your area".


It was sent to customers all over the country even though the Glo-Bug system is available only in Auckland.

Mr Munro said the company made a mistake and has apologised to 18,000 of its 305,000 residential customers.

"The mistake is that the letter went to a large number of clients who have an otherwise good credit history with Mercury but for whatever reason have missed paying their latest bill," he said.

"I have written to all those customers that shouldn't have got that letter, that should have got a standard reminder, to apologise to them."

Meanwhile, Counties-Manukau Grey Power vice-president Ron Wilkins has started a petition against Mercury's charges, introduced in July last year, for paying power bills by cheque (50c), credit card ($2.50) or over the counter at Post Shops ($1.50).

He said many elderly people could not afford the internet and did not like paying by direct debit.

"We are old-fashioned and we like to collect our money in cash and pay the power bill, the phone bill and the other bills and have a cup of coffee in town and catch the bus home. We have a day's outing," he said.

"A lot of other people I have spoken to don't trust the banks. They get their money out and physically pay their bills."

Mercury is one of only five out of 14 electricity retailers that charge a fee for payments over the counter. Meridian also charges $1.50 for those in its "Heaps of Choice" pack, Trust Power charges $1.38 and Nova Energy and Bay of Plenty Energy charge 50c.

"We are charged $1.60 by NZ Post so we subsidise it," BOP Energy said.

There are no charges for over-the-counter payments for Contact, Empower, Energy Online, Genesis, Just Energy, King Country Energy, Powershop, Pulse Energy or Mercury's Cambridge-based rural sister Tiny Mighty Power.

However, Mr Munro noted that Contact recently introduced a 22 per cent prompt-payment discount only for customers who paid online, disadvanaging those who paid over the counter.