HSE managers, who are members of the Fórsa trade union, have resumed industrial action.
The union had suspended action earlier this year in response to a recruitment pause and talks were under way at the Workplace Relations Commission.
However, it decided to resume industrial action after the HSE announced an immediate freeze on filling new and replacement management posts to control budget overrun.
It said members would not undertake tasks or responsibilities associated with any vacant post from today.
Members will also not carry out duties of a higher grade and will boycott discussions on health region reforms.
The HSE is "targeting" clerical administrative posts instead of addressing agency costs, Head of the Health and Welfare division in Fórsa Ashley Connolly, has said.
Speaking on RTÉ's Morning Ireland, she said the HSE claims that its decision to impose a full recruitment ban and moratorium on the replacement of all clerical administration posts is "solely related" to their budget overrun.
Administrative staff are being scapegoated for "mismanagement" by the HSE, Ms Connolly said.
"What they have failed to address is the overrun in terms of agency cost, but more importantly the external private consultants and the excessive costs to the HSE on using the likes of external private consultants for advisory functions.
"This is not acceptable. It is a pure waste of taxpayers money."
Industrial action will "undoubtedly" have an impact on services, HSE HR Director Anne-Marie Hoey said.
On the same programme, she said procedures are in place at a local and national level to "manage" the dispute.
"We want to ensure there is no risk or impact on our patients or critical support services.
"If our assessment demonstrates that there is such a risk, derogations will be sought through our dialogue with Fórsa to ensure the protection of services and to ensure there is no risk to patients or emergencies through this dispute."
The HSE will continue to work through the dispute mechanism and that they remain available for discussions at the Workplace Relations Commission, Ms Hoey said.
It received funding this year for 1,460 new jobs in management administration, she said, describing the level of investment as unprecedented.
"This brings to 6,000 the total increase in new management administration staff since 2020," she said.
