More than 6,000 hospital patients face cancellation of treatments and procedures after striking health staff vowed to ramp up their pay row with a three-day walkout next week.
Siptu has also threatened to escalate the industrial action further with a five-day stoppage between Monday and Friday the following week.
It follows yesterday's strike action by 10,000 healthcare support staff in 38 hospitals, which led to thousands of patients having surgeries and investigations cancelled.
Hospital emergency consultants warned that a three-day strike would pose serious dangers to patients in A&E departments and could not be tolerated.
Dr Emily O'Conor, an A&E consultant at Connolly Hospital Dublin, said it had proved difficult to maintain services yesterday despite all staff stepping in to do duties such as cleaning up bodily fluids and taking blood products to resuscitation patients.
"For parts of the hospital that cannot postpone care the three-day strike cannot happen. If it does, emergency departments need a derogation," she warned.
The dispute may worsen as 24-hour strikes are scheduled next Tuesday, Wednesday and Thursday, and industrial action could spread to 58 hospitals and healthcare facilities by the end of the month.
All children's hospitals and care of the elderly and intellectual disability facilities could be hit as the union has threatened to ballot another 10,000 staff for strike action.
The first 24-hour strike by staff including porters, healthcare assistants and chefs led to 2,000 patients having appointments for surgery, scope investigations and out-patient care postponed.
Managers, doctors and nurses had to help feed patients and transfer them between wards.
Families spent hours providing care to loved ones and brought in meals from home to supplement the sandwiches and soup that some hospitals were reduced to serving.
Siptu health divisional organiser Paul Bell warned that next week's strikes will not be deferred despite fresh talks at the Workplace Relations Commission planned for today.
He also revealed the union's plans to escalate industrial action to a full week's strike the following week.
"The three strikes next week are extremely likely to go ahead," he said.
"If we ballot, all of the children's hospitals, care of the elderly facilities and intellectual disability facilities will be included. We are talking about probably another 10,000 people.
"It will take some moderation of the employer's attitude, never mind offer, to make progress."
He accused the Government of attempting to dismantle a job evaluation process at the core of the dispute.
The support staff want pay rises of between €1,500 and €3,000 that they say are due under the assessment.
"The evaluation is more serious than money at this stage," Mr Bell said.