Electric Ireland has said it is withdrawing from the Northern Ireland domestic electricity market to concentrate on business customers.
The Irish company is the third-largest supplier in Northern Ireland, with more than 50,000 domestic customers.
A company statement said it has completed a strategic review of its residential businesses.
It added: “As a result of this review, we will be focusing exclusively on the business market and, over time, our intention is to no longer serve the residential market.
“Electric Ireland will continue to supply and support our residential customers during this transition.
“This will involve working collaboratively with key stakeholders, including the Utility Regulator, and with our residential customers to ensure a managed approach.
“During the process, Electric Ireland will continue to supply our (circa) 53,000 residential customers, equating to 6% of the market.”
The firm said it understood the news would be unsettling for some customers but said there would be no interruption to supply and customers do not need to take any action.
Electric Ireland also said there are no immediate job losses planned.
Alliance Party MLA David Honeyford said the announcement raised a number of “very serious concerns”.
He said: “It is worrying to see any kind of competition removed from the energy market here, and we must get reassurance from the Utility Regulator that Electric Ireland’s removal will not lead to anything approaching a monopoly, which could be a disadvantage to both the public and potentially also businesses operating from domestic premises too.
“We must now see the incoming Economy Minister (Deirdre Hargey) take swift and urgent action to ensure the rights of workers and consumers are upheld at every juncture going forward, that their interests are protected, and that they’re adequately supported through this transition to come.”