Commercial lawyer Stephen Franks believes there is a good chance the Commerce Commission will review how it calculates the amount of profit that Transpower and lines companies can make.
The Major Electricity Users Group says a High Court decision has identified an error in the way the profit is now set, which has resulted in customers being overcharged by more than $150 million per year.
It says this must be urgently addressed.
Mr Franks, who represented the group in the High Court, says if a review is not conducted by the end of next year, the rules that lines companies currently operate under will remain in place until 2020.
He says the net effect of that would be a windfall for the companies of about $1 billion over 10 years.
