About 30 owners gathered in Dunedin last night to discuss the power company's botched marketing campaign, despite Mercury's decision not to send a representative to the meeting.
Otago Chamber of Commerce chief executive John Christie told the meeting he had a draft legal opinion that suggested the company's original offer was binding.
Mercury representatives contacted 410 business owners across Dunedin last month, offering huge discounts - in one case 30%, saving $16,000 a year - to those who agreed over the telephone to switch providers.
Verbal contracts were agreed and letters of confirmation sent, before the company began calling again and withdrawing the offer, blaming a pricing error.
The draft legal opinion, from Gallaway Cook Allan in Dunedin, indicated three areas in which Mercury's decision to withdraw the offer could be challenged, Mr Christie said.
On balance, it appeared "there is a legal case that could be taken to hold Mercury to the deal", he said.
"They believe there's a good chance [Mercury] would have to hold to that deal."
The information would be sent to business owners and a second meeting held at the chamber's office later this week, with a Gallaway Cook Allan representative there to explain the legal options.
Those options were to seek an injunction to force the company to honour the deal, or a claim for damages, Mr Christie said.
Mercury has since offered a revised discount, representing half the original savings, and had sent staff to Dunedin to hold one-on-one meetings this week.
Mr Christie said he was "disappointed" Mercury staff missed yesterday's meeting, and would be inviting them to the next meeting and calling Mercury general manager James Munro this week.
Mercury staff could not be contacted last night.
