The Irish Nurses and Midwives Organisation has pledged to support non-consultant hospital doctors if their threatened strike over excessive working hours goes ahead next week.
The INMO Executive Council has unanimously decided to advise members not to do any work normally carried out by doctors during a 24-hour stoppage planned for 25 September.
The union condemned the HSE for failing to implement the European Working Time Directive for junior doctors.
INMO General Secretary, Liam Doran said the HSE was clearly in breach of both Irish and EU law - and was exposing the state to very substantial EU fines for its continued failure to meet deadlines for implementation.
He said it was unacceptable that the doctors had been forced into dispute in order to achieve safe working hours.
Mr Doran said that under the Haddington Road Agreement, the INMO had worked with the IMO to offer potential solutions, but claimed the HSE had shown little or no interest so far.
He said the INMO would not allow nurses and midwives to be used to undermine the IMO in their legitimate dispute.
Talks aimed at averting next week's strike between the HSE and the IMO have resumed at the Labour Relations Commission.