Nurses at Dublin's Beaumont Hospital have served notice of industrial action, due to what they say are unsafe conditions in the Emergency Department.
It will start with work to rule on June 10, when nurses attached to the INMO will refuse to carry out non-essential or administrative duties.
They stress that essential care for patients will be provided.
The union agreed to defer industrial action earlier this year, after agreement at the LRC on increased staffing and other measures to tackle overcrowding in the ED.
But Lorraine Monaghan, industrial relations officer with the INMO, said they were not implemented.
"Agreement was reached last January in respect of additional staffing and measures to address the overcrowding in the department, however those measurements have not been implemented," said Ms Monaghan.
"The staff that have been promised have not been recruited although four months have passed. So the department is constantly understaffed even though it is dangerously overcrowded."
“It is a disgrace that both patients and staff are exposed to such appalling conditions in
this day and age,” she said.
“This unsafe situation has to be addressed, once and for all, in the interest of safe patient care and the health and safety of staff working in the department’."