The Irish Medical Organisation has said that it will resume planned strike action next Tuesday, 8 October, over "dangerously" long hours for junior doctors.
The day of action was deferred last week to allow talks with the HSE progress and the IMO said the strike will affect all public hospitals.
The development follows what the IMO claims has been a lack of clarification from the HSE on several issues during talks over recent weeks at the Labour Relations Commission.
The union said a key issue was a refusal of the HSE to accept realistic financial sanctions for failing to comply with the European Working Time Directive.
The IMO wants an immediate end to shifts of over 24 hours and clarity on how the HSE will meet its commitment to ensure no doctor works longer than 48 hours a week by the end of next year.
It said a recent survey of work patterns shows that 85% of NCHDs work shifts of over 24 hours.
The HSE has insisted that significant progress has been made in cutting junior doctors' hours and that the average working week for junior doctors is now 54 hours.
It claims 34% of these doctors are working shifts of over 24 hours.
But it has said that reducing hours in smaller hospitals is posing a challenge.
The IMO represents around 3,000 of around 4,700 NCHDs in the country.
In its recent ballot, over 97% of 1,000 NCHD members backed industrial action.
HSE expresses 'surprise and disappointment'
The HSE has said it was surprised and disappointed with the decision of the IMO to serve strike notice.
It said significant progress had been made in talks at the LRC.
The HSE said that strike action would only serve to create significant disruption for patients.
Meanwhile, it has emerged that in its proposed agreement put to the IMO today, the HSE promised a maximum of 24-hour shifts by 30 November, other than in exceptional circumstances, with full implementation by 14 January 2014.
It also promised full compliance with the European Working Time Directive of a 48-hour week by the end of December next year.
There would also be joint IMO-management verification and implementation at national and local level, as well as a referral of a range of other items to the LRC.
As a sanction for hospitals if they failed to end shifts over 24 hours, the IMO had sought the granting of extra paid leave to junior doctors.