Small business and large energy users could see an increase in what they pay for electricity to cover the cost of upgrading the grid.
The Utility Regulator said the work should cost £2.21 billion between 2025-2031.
It said NIE Networks is responsible for building and maintaining electricity transmission and distribution networks, which allows consumers to access a secure supply of electricity.
As a natural monopoly, it said NIE Networks is subject to economic regulation which provides protection for all electricity consumers in terms of quality and cost.
John French, Utility Regulator chief executive, said the upgrade will create the foundation for Northern Ireland’s journey towards net zero and will facilitate a more efficient use of the electricity system.
He said the additional investment will increase the network cost for electricity consumers, and they have made proposals within a draft determination to ensure the transition is “affordable, fair and inclusive for all”.
The proposals include that dependent on usage small businesses could see a 3%-9% increase, whilst large energy users could see an 11%-19% increase on the network element of their bill.
The draft determination is open for consultation until March 22, 2024.
Manufacturing NI chief executive Stephen Kelly slammed as “frankly scandalous” that the largest energy users could see their bills rise by up to 19%, and said they are seeking an urgent meeting with the regulator.
“NIE Networks made an operating profit of £117 million last year passing a dividend to ESB in Dublin of £37 million,” he said.
“This is an eye watering margin of 39% but even after finance costs their margin was still 25%. Levels their customers could only dream of.
“We have also seen our electricity generators secure obscene profit levels to the point where governments have introduced new emergency tax powers.
“The Regulator’s own analysis shows that local firms already pay the second highest energy bills in Europe, significantly higher than in GB or Ireland. This is hugely damaging to our economy and our ambitions.”