ESB Electric Ireland said today that the vast majority of accounts facing a new "low user standing charge" relate to vacant buildings or holiday homes.
Any customer whose premises uses an average of 2 units or less per day will be eligible for the charge, which could add another 15½c on to the daily cost.
It is expected that around 100,000 accounts will be affected.
Corporate communications manager Brian Montayne said that rather than raising the cost for all customers, ESB Electric Ireland is trying to target accounts which causing the firm to lose money.
"In analysing those accounts, we've established that there is an underecovery in those particular accounts, and rather than, I suppose, introduce any changes across the entire customer base, we've decided to focus on the accounts that are directly responsible," he said.