Workers at the company which ensures electricity is supplied to homes and businesses in Northern Ireland have threatened to take industrial action next month which could involve a strike.
Trade union Prospect, which represents workers at the System Operator for Northern Ireland (SONI), said it's worried there could be disruption to the public.
The union and SONI - owned by Irish company Eirgrid - are at loggerheads over pay. Prospect said SONI staff have not had a pay rise since 2015. A union spokeswoman said: "Unless they change tack and fast, we are heading into a prolonged period of industrial action. This will have negative impacts on Northern Ireland at the worst possible moment. We have taken steps to ensure any action does not harm the safety of the public but we are still concerned about the disruptive impact of any action."
Prospect said 90% of its 100 members on the SONI workforce voted in favour of industrial action, up to and including a strike.
It's understood SONI is working on contingency plans to ensure any potential strike does not disrupt supply.
Robin McCormick, SONI general manager, said: "SONI regrets that union members have opted for this course of action, particularly as the company recently invited all union representatives to participate in independent arbitration through the Labour Relations Agency.
"SONI has also made what we feel is a fair pay offer which has been rejected by the union.
"We want to emphasise that we are keen to continue engagement with Prospect and to work through the offices of the Labour Relations Agency (LRA) in order to reach a satisfactory outcome for all involved. The offer of independent arbitration remains on the table and we call on the Prospect Union to withdraw the industrial action notice and to accept our offer of talks through the LRA.
"In the meantime, our priority is to continue to maintain a secure supply of electricity to homes and businesses across Northern Ireland at the least possible cost."