The nurses' dispute is going back to the Labour Court after talks between government and unions broke down.
The INMO has rejected the government's draft contracts as "unreasonable".
A ballot of union members which had been due to take place yesterday but union bosses said it would be postponed by two weeks.
INMO general secretary Phil Ní Sheaghdha said the sides were very far apart.
"We have made some very clear suggestions and amendments and put them forward and the sides are very far apart," said Ms Ní Sheaghdha.
"The executive council have today considered the matter and it is now agreed that the matters will be agreed to the Labour Court and the Labour Court will be asked to look at the positions."