Thousands of health workers are set to take industrial action from next week over new arrangements in the health service.
The trade union Impact said its members had not received adequate assurances about the arrangements which take effect from January.
The union, which represents 25,000 health workers, added that its members would not co-operate with the changes being made.
In a letter to the Health Service Employers Agency today, IMPACT's National Secretary, Kevin Callinan, said health staff needed more detailed safeguards before the action could be called off.
However, the letter did accept that it was not impossible to address all the issues before 1 January.