A one-day strike by up to 500 ambulance personnel which was scheduled for next Wednesday has been deferred until 22 January.

The dispute centres on the HSE'S refusal to recognise their union - the Psychiatric Nurses Association - for negotiating purposes, or to deduct PNA union subscriptions through the payroll system, as it does for other unions.

The 1,800 personnel in the ambulance service were traditionally represented by SIPTU and Fórsa.

However, in 2010 a breakaway group called NASRA was formed, which subsequently affiliated to the PNA.

They now claim to represent 500 of the 1,800 ambulance service employees.

However, the HSE has insisted that the PNA does not have negotiating rights for the grades in question.

Today the PNA said the decision had been taken on legal advice.

It is understood that this followed legal correspondence from the HSE.

The PNA accused the HSE of not only refusing to negotiate with the PNA when representing its ambulance branch, but also of refusing to negotiate contingency plans for the planned industrial action.

The PNA said it was now seeking an urgent referral to the Workplace Relations Commission.

Separately, the PNA has deferred until Monday announcing the result of its ballot for strike action by up to 6,000 psychiatric nurses following their overwhelming rejection of Government pay proposals to address staff shortages in nursing.