ESB Networks technicians belonging to the Independent Workers Union have extended their pickets to work locations which had not previously been picketed.
The union claims to represent over 500 of the company's 1,500 network technicians.
It said extending their pickets could increase the risk of disruption for customers, as workers from other unions who were previously free to work in those locations may refuse to pass pickets.
The IWU network technicians commenced their latest two-day strike at 8am, which they say centres on the company's failure to consult adequately on the outsourcing of certain work.
IWU Regional Secretary Gerry Corbett insisted that the strikers were getting support from members of recognised unions, who were refusing to pass the pickets even though their unions - Connect, SIPTU and Unite - are not involved in this dispute.
ESB Networks has refused to disclose how many network technicians refused to turn up for work on the two previous strike days.
A spokesperson for ESB Networks said that customer impact this morning was "very low".
He said that pockets of customers had been left without power yesterday because of the windy weather, but said restoration times were in line with business as usual.
Mr Corbett said the IWU would be conferring with its legal team this evening, and will hold a meeting of its Strike Committee tomorrow evening to decide their next move.
He said they were not going to fall into a trap of "ongoing, ongoing" industrial action - adding that the union was looking at a Plan B which would be "very unexpected".
ESB Networks has acknowledged that industrial action by some network technicians has caused limited impact to customers, but has declined to specify the extent of that disruption.
Yesterday, it called on the IWU to cancel today's stoppage.
The network technicians belonging to the Independent Workers Union have been engaged in a work to rule since 19 April, and have also held two 24-hour strikes.
They say the dispute is over the right to be consulted about outsourcing of certain work to private contractors - and claim to represent over 500 of the company's 1,500 network technicians.
However, the company does not recognise the IWU, which rejects suggestions that the dispute is really over union recognition.
Last week ESB Networks issued legal proceedings against the IWU for defamation, conspiracy, inducement of breach of contract, unlawful interference with contractual relations and unlawful interference with its business.
In an update on the industrial action issued yesterday, the ESB stated: "We again call on the IWU to desist from further action at this time of national need."
It described the industrial action as "unnecessary".
It said that contingency planning was continuing for the next 48 hours "and beyond" and that it was working to mitigate any impact on customers.
It expressed concern that the IWU had not co-operated with emergency cover since the action began two weeks ago, stating; "This is unprecedented in ESB's experience."
ESB Networks said real time updates on electricity faults could be found on www.powercheck.ie.
The company acknowledged what it called the "strong support" provided by staff belonging to affiliated trade unions (Connect, SIPTU and Unite) who have said they are not involved in this dispute.