Ambulance drivers might be told to strike by the General Workers' Union, unless certain work practices are changed.
The union took another step towards a strike - issuing fresh directives - on Thursday, saying that it was objecting to various issues, such as the way in which overtime was organised, work which fell outside job descriptions, and poor maintenance equipment.
It also said that certain procedures were being changed without it being consulted.
The union gave no deadline and it also said that the directives currently in force have no impact whatsoever on the service to patients and those who use the ambulance service.