Nurses at Naas General Hospital, who are members of the Irish Nurses and Midwives Organisation, have begun industrial action.
The work-to-rule action is in a dispute over staffing numbers.
The INMO said that current staffing levels across multiple clinical areas are unsafe, unsustainable and non-compliant with professional standards.
Members will also hold a lunchtime protest outside the hospital as part of the action.
"INMO members are dealing with immense pressure, unsafe conditions and continuous redeployment to different clinical areas in order to fill the most dangerous staffing gaps," said INMO Assistant Director of Industrial Relations Bernadette Stenson.
"Nurses in Naas do not want to take this action, but they see no alternative if there is to be meaningful change in the hospital and significant measures taken to ensure their safety and the safety of their patients," she added.
In a statement, the HSE said it regrets the action is under way.
It said that while discussions between the parties to date have not resulted in agreement, the HSE remains willing and available to engage constructively with the INMO at any time in order to reach a sustainable resolution.
It said the hospital has put a range of measures in place to manage services and minimise disruption during the period of industrial action.
However, it has advised patients and the public should be aware that there may be some delays to patient flow through the hospital as a result.
The hospital said that there has been significant growth in the hospital workforce in recent years.
"Total staff numbers increased from 796 Whole-time equivalent (WTE) in December 2021 to 1,008 WTE in November 2025 - an increase of 212 WTE, or 27%, over four years.
"Approved nursing staff numbers have grown from 358 WTE in December 2022 to 433 WTE in December 2025, representing an increase of 75 WTE, or 21%.
"Additional nursing staff posts have recently been approved for Safer Staffing posts (16 WTE) and there are further plans to progress longer-term measures to support and strengthen nursing capacity and enhance the overall service delivery model," the HSE said.
The HSE added that it fully recognises and sincerely appreciates the continued professionalism, flexibility and commitment shown by staff at Naas General Hospital.
