The Taoiseach has called on the Health Service Executive to "properly manage and deploy" resources in the health service over the Christmas period.
Speaking at a press conference in Finland, Leo Varadkar said that it makes sense to match peak demand with peak resources.
He was speaking after being criticised for comments he made in the Dáil yesterday, when he said that hospital consultants, nurses and other medical professionals should not be on extended leave over Christmas and the first two weeks of January to ensure that every hospital bed is open.
Mr Varadkar said that a huge amount of additional resources have been added to the health service in the last two years, and that proper management of the resources is needed.
"So it should be obvious to everyone that more money, more staff, more beds on its own won’t work," he added.
"We need to properly manage and deploy those resources when they are most needed, and that’s what I’m saying to the HSE that I want them to do."
The organisation representing consultants has rejected Mr Varadkar's claims about festive leave.
In a statement Dr Donal O'Hanlon of the Irish Hospital Consultants Association said he was "extremely disappointed" with Mr Varadkar's remarks.
The General Secretary of the Irish Nurses and Midwives Organisation described the Taoiseach's comments as an attempt to divert from the real issues.
"Despite the comments, there is absolutely no doubt that the most significant issue in the health service is the lack of capacity in our public hospitals," he said.
"The trolley crisis is not just over the Christmas period. The lack of capital investment in our public hospitals has resulted in a year-round crisis for hospitals which are struggling without the means to provide a proper standard of care to their patients."
Phil Ní Sheaghdha said the real issue is that there is no winter plan and said this winter is going to be as bad, but hopefully not worse, than last year.
Speaking on RTÉ's Today with Sean O'Rourke, she said INMO members work 365 days a year and many have built up a considerable amount of hours that they are owed.
She said one department in one hospital has 1,000 hours owed.
Ms Ní Sheaghdha said annual leave is curtailed over periods like Christmas and hospital rosters are "totally dependent on agency (staff) and overtime".
She added that the healthcare system is also dependent on goodwill during crisis periods, such as Storm Emma in March, because the system is unprepared for such periods.
Earlier, the President of the Irish Medical Organisation said that annual leave was not a contributor to the overcrowding problem in Irish hospitals, which manifests in the emergency departments.
Speaking on RTÉ's Morning Ireland, Dr Peadar Gilligan said that the issue is a lack of capacity.
He added that it would be more helpful to see a strategic plan to increase capacity and recruitment in health staff, than blaming doctors and nurses for the challenges in the health care system.
Attacks on health staff will not help with recruitment problems, he said.
Dr Gilligan said if he honestly believed that working over Christmas and New Year period would help resolve the problem, he would strongly consider it, but the reality is that is not the problem.
Sinn Féin has also hit out at the Taoiseach's comments.
Speaking during Leaders' Questions in the Dáil, Sinn Féin's David Cullinane said Mr Varadkar attempted to put the blame for hospital overcrowding on the shoulders of frontline staff in hospitals.
He said: "Nurses and doctors leave is not the problem here, it does not contribute to hospital overcrowding.
"The problem is capacity in our public health services".
Minister for Agriculture Michael Creed, who was taking Leaders' Questions on behalf of the Government, said the Taosieach's comments were evidence that the Government's priority is to make sure that it deals with patients in an effective, humanitarian way.
He said the comments demonstrated that frontline staff are critical to resolving the problem of overcrowding and "far from denigrating them, the challenge the Taoiseach posed was to HSE management" to appropriately manage human resources in the health services.
Labour Party leader Brendan Howlin said that Mr Varadkar should not have blamed health staff for taking their annual leave.
Also speaking in the Dáil, he said that the rostering of staff was a management issue, which "should have been addressed by constructive engagement with unions, and not by abusing staff on the airwaves or in the House".