The ongoing work-to-rule by nurses in the south east is beginning to make normal services difficult to sustain, the Health Service Executive has said.
In a statement, the HSE said the action by the Irish Nurses Organisation (INO) and the Psychiatric Nurses Association (PNA) "continues to cause disruption" and it apologised to the public for the inconveniences being caused.
"The HSE are continuing with preliminary talks with the INO and PNA. The work-to-rule is affecting services to patients - particularly efficient clinical communication - and is causing difficulties and inconvenience for those who are depending on the HSE for essential services," the HSE said.
It acknowledged the "enormous" efforts made by all staff who were working to fill the "gaps" opened up by the action but added: "The system is coming under considerable strain and, as the action is now in its fourth week, it is beginning to make the normal service levels increasingly difficult to sustain, without compromising patient care and increasing levels of risk for patients.
"In many cases, people are working many hours beyond their normal commitment."
The HSE said that where it might be necessary to change patient appointments, they will be contacted directly and that there is no need for them to contact the HSE first.
Non-urgent elective surgeries at Waterford Regional Hospital, which were previously being deferred, have now returned to normal, the HSE said.
"In regard to the other acute hospitals in the south east - namely South Tipperary General (Clonmel), Wexford General and St. Luke's General (for Carlow/Kilkenny and including Kilcreene Orthopaedic) - normal services are ongoing (i.e. no procedures deferred, clinics running as normal etc). This is in the context of a general slowing of systems in the circumstances."
Members of the public were urged to keep phone contact to HSE services "at a minimum".
It said the situation will be reviewed on a daily basis.
"The HSE values the support of all its staff, appreciates the co-operation of the public and wishes to assure them both that efforts are continuing to find a way forward that is sustainable and agreeable to all parties."
Talks between the nursing unions and the National Implementation Body, the State's trouble-shooting mechanism for industrial relations issues, are continuing.