The head of the health and welfare division in trade union Fórsa has called on management at the Health Service Executive for "timely engagement" in relation to members working on a voluntary basis and a possible seven-day roster.
It comes after Chief Executive of the HSE Bernard Gloster said seven-day provision of healthcare is central to the effort to improve services across the country.
Speaking at the Fórsa health and welfare conference in Galway yesterday, Mr Gloster said there was "incontrovertible evidence" that the level of staffing at weekends and public holidays was below what was needed by the public.
He asked delegates to assist in the move to distribute services more evenly across the full week.
Separately, Minister for Health Stephen Donnelly said he has a draft Urgent Care Plan from the HSE to deal with overcrowding in emergency departments.
Speaking on RTÉ's Morning Ireland, Fórsa's Ashley Connolly said: "We need to see the real detail if we are to have a sustainable plan. We need to see what the proposals entail."
She said the sooner management present them with detail they can allay their members' fears.
Ms Connolly criticised ad hoc arrangements being put in place in different hospitals.
"That is not continuity of care.....that is not providing the best care that can be delivered," she said.
"What we really need to do is look at is there a willingness and is there a possibility of a sustainable plan that can be delivered."
She warned that it will not be delivered if their members' voices "can't be heard in that".
She said it is important their ideas and solutions can be put forward to see what can be delivered as part of the overall plans.
She said Fórsa will not be found wanting in terms of engagement but "members have a genuine fear when you hear seven over seven".
Ms Connolly also said the level of detail required has not been passed on to trade unions about requests to work this June bank holiday weekend.
She said whenever there is a call for members to deliver additional services, services have "not been found wanting".
"They have always been willing to do so on a voluntary basis," she said.
Ms Connolly added that members have not had any firm proposals put forward to them in terms of pay.
"What the CEO did say was that there may be engagement in advance of pay talks," she said.
"And we are available to have those discussions."
Meanwhile, the Irish Medical Organisation's consultant leader Professor Matthew Sadlier said that if every bank holiday is a crisis, then volunteering is not the answer.
He said there needed to be an increase in capacity both in terms of beds and staffing levels to deal with the number of patients attending.
Prof Sadlier said that doctors can only legally work a certain number of hours a week.
Meanwhile, the Chief Executive of the Saolta Hospital Group has said they are using the situation in hospitals over the May bank holiday weekend to prepare for the upcoming June bank holiday weekend.
Speaking to RTÉ's Morning Ireland, Tony Canavan, said their first preperation has been to assess "what worked well and what didn't work well".
He outlined how during the May bank holiday weekend it went from a situation where there were available beds to the number of patients increasing sharply and then being on trolleys.
He said they have to learn from experience and go into this next bank holiday weekend with a low level of delayed discharges and working with staff to increase the level of service and level of discharge.
He cautioned that it is not good enough to just discharge people but ensure they can do it efficiently and safely, taking into account the pathway of care for the patient.
He said it is very important the health service works together to ensure it operates effectively and he described a need for change so there is a seven day structure in place to meet the needs of patients.
He said people are coming into Emergency Departments in increasing numbers over weekends and bank holidays.
He added that changing rosters is one way to resolve this and that means engaging with unions and staff.