Ambulance personnel belonging to the Psychiatric Nurses Association are to strike for three further days over the coming weeks in their dispute over union representation.
Traditionally, around 1,800 paramedics were mainly represented by SIPTU, but in recent years up to 500 have broken away to join the National Ambulance Service Representative Association (NASRA), which is affiliated to the PNA.
However, the HSE has refused to negotiate with the PNA/NASRA on the grounds that it already recognises a number of unions within the National Ambulance Service.
It said to recognise more would impair good industrial relations.
The PNA members have already taken one day of strike action, but with no breakthrough in the dispute, the union has announced three further days of industrial action.
They will strike from 7am to 5pm on Friday 15 February, with two consecutive strike days on Thursday 28 February and Friday 1 March.
PNA General Secretary Peter Hughes acknowledged the strikes represented a considerable escalation of the industrial action to date.
He said it demonstrated their resolve to be represented by the union of their choice and not by a trade union that the HSE wanted to force them to join.
He also accused Minister for Health Simon Harris of complete indifference to the dispute.
The union called on the minister to instruct the HSE to engage with the industrial relations machinery to allow ambulance personnel the right to be represented by the trade union of their choice.