Public health doctors are to step up industrial action next week in a row with the Government over a delay in introducing reforms.
The doctors, all of whom work in the public sector, are seeking better pay and the implementation of a report published last April which recommended that they be on call around the clock to deal with threats to public health.
The main work of public health doctors includes the surveillance and control of infectious diseases such as meningitis, the winter vomiting bug and food poisoning.
They are also responsible for public health programmes such as vaccinations and screening programmes and strategies dealing with heart disease, cancer, accidents, tobacco and drug misuse.
The doctors, members of the Irish Medical Organisation (IMO), are currently on a work-to-rule over what they claim is the Government's failure to "negotiate constructively" on a number of issues.
This has involved refusing to participate in planning to deal with bio-terrorist threats.
The IMO says employers have failed to organise on-call rosters to enable public health doctors to heighten preparedness for such threats, as well as manage infectious diseases on an out-of-hours basis.
Senior public health doctors should also get the equivalent pay of hospital consultants, the union claims.
Extended actions, to be implemented from next Monday, will include doctors stepping down from acting positions and a refusal to co-operate with new work practices or programmes.
Dr Joe Barry, the IMO's public health committee chairman, said services to the public would be affected if the dispute dragged on.
"Health services such as the surveillance and control of infectious diseases, vaccinations and other preventive health programmes, already overstretched, could face further deterioration should the dispute continue indefinitely."
The IMO had also sought a meeting with the Minister for Defence, Mr Smith, to brief him on Ireland's "lack of preparedness for a bio-terrorism threat," he said.
The Department of Health described the doctors' action as "unacceptable".
It said there were issues to be addressed in accordance with established industrial relations machinery and "in the context of Government pay policy".