Business owners contacted yesterday remained angry at Mercury's refusal to honour the deal, despite reaching verbal agreements by telephone and sending written confirmation to companies across the city.
Those contacted said they were now considering legal action, an appeal to the Electricity and Gas Complaints Commission and - in one case - partially withholding future power payments to the company until taken to court.
It also emerged yesterday Genesis Energy made a similar mistake earlier this year, offering incorrect discounts to 16 residential customers in Dunedin.
However, the company decided to honour the discounts, despite the error, Genesis public affairs manager Richard Gordon, of Auckland, confirmed.
"We believe this is the right thing to do for our customers."
His comments came after the Otago Daily Times yesterday reported Mercury had offered 400 businesses across Dunedin discounted power if they agreed, over the phone, to switch providers.
The company on Thursday confirmed it had withdrawn the offer because it contained a "pricing error" that failed to account for local line charges.
Businesses said they were told the offer was meant for Dannevirke, not Dunedin.
The company apologised and offered to automatically return customers to their previous providers. Those who would still save money with Mercury could choose to remain with the company.
However, Mercury staff would not rule out honouring the deal when asked yesterday.
Mercury communications manager Marie Hosking was asked if the company was reconsidering its position, or whether it could rule out honouring the deal.
In response, she would only say the company would "continue to deal with these customers on an individual basis".
However, Otago Cleaning Supplies owner Peter de Clifford told the ODT he contacted the company yesterday and was told the matter was still being considered by management, with more information expected next week.
Mr de Clifford believed an agreement by the company to honour its original offer was only "a possibility".
"I wouldn't say it's a likelihood."
Some business owners were preparing to fight, with Kaan's Catering Supplies owner Lindsay Kaan - who was offered a 30% discount, saving $16,000 a year - considering withholding part of future power payments until he was taken to court.
Other owners planned to meet next week to discuss a joint approach, and legal advice would be sought, he said.
Ironic Cafe and Bar owner Steve Wilson - offered a 30% discount, saving more than $3000 - said he was considering an appeal to the Electricity and Gas Complaints Commission, and legal action "could be an option".
Otago Chamber of Commerce chief executive John Christie said he would canvass businesses next week to gauge the size of the problem, and would consider approaching Mercury on their behalf if requested.
It would be "ideal" if Mercury decided to honour its offer, but he did not know what the legal position was.
It might be unrealistic to expect Mercury to take a financial loss in honouring the offer, but "they should be trying to find a middle ground that's fair for them and fair for the customers of Dunedin", he said.
Calls to honour the deal were backed by Genesis customer Christine Philp, of Dunedin, yesterday.
She was one of the 16 customers offered a faulty discount by Genesis, only to have the deal honoured, and believed Mercury should do the same.
"It's basically the same position, but they [Genesis] honoured it," she said.
Business owners spoken to yesterday also confirmed Mercury's rivals, Genesis and Contact Energy, were approaching disgruntled business owners yesterday offering their own discounts.
Contact staff would not elaborate yesterday, while Mr Gordon would only say Genesis was "working hard to sign up new business and residential customers in the city".
Ms Hosking said Mercury acknowledged its "genuine mistake".
"We sincerely apologise to those customers affected. We have put the necessary systems in place to reduce the risk of this happening again in future."
