The Children's Hospital in Tallaght is reopening this morning.
Acute services for children were temporarily relocated to Crumlin and Temple Street in March to support adult services at Tallaght to deal with the initial COVID-19 surge.
This morning the hospital will be back operating services including the 24/7 Emergency Care Unit, medical inpatients, x-ray and outpatients.
However, critically ill and critically injured children will be redirected to Crumlin and Temple Street.
Children's Health Ireland says it's an acceleration of some of it's original plans to consolidate specific services and to use a city-wide approach across Crumlin, Tallaght and Temple Street for others, including access for medical admissions.
However the INMO has described the move as a "sudden and unplanned" downgrading of services.
The union, which represents nurses and midwives, says the changes will see all acute paediatric surgical services immediately withdrawn at Tallaght, diverting roughly 6,000 additional cases to Crumlin and Temple Street.
It says neither of which have been given additional resources to cope.
"INMO members only became aware of this when they arrived to work on Monday morning, with no prior warning or discussion" he said.
