"I don't want to go on to it. The way I do it now is I pay the bill late. With Glo-Bug, what happens if you find you haven't got any money today and your power stops?"
Ms Hepple, 48, worked for 14 years as an administrator with the Auckland Philharmonia, but has not been able to get a job since she had to stop work with breast cancer in 2001. She said she would pay her bill to avoid going on to the pre-pay system but she feared for others who would be forced on to it.
"I've heard so many bad things about it," she said.
TVNZ's Fair Go reported last year that Mercury originally did not charge a daily fixed rate for the service but introduced a fixed rate last year.
It also changed its meters from showing how much credit was left to a system showing a green light when customers are still at least $10 in credit, an orange light when the power was due to be disconnected the next day and a red light when it would be cut off at midday that day.
Mercury's head of credit for commercial and Glo-Bug, Luke Blincoe, said the company changed its policy last month to "include a statement about Glo-Bug earlier in our processes".
"As an energy provider in a competitive industry, we cannot 'force' customers to accept any specific product," he said.
"What we can do is exercise judgment over which customers we can responsibly extend credit to, as we don't believe it is in anyone's interests to allow customers to accrue large debt. As a result, in some cases we may limit our offer to pre-payment only.
"We would be disappointed if customers chose to move to another retailer, but we accept that is their right."
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