HSE support staff at Mayo, Galway, Roscommon and Sligo University Hospitals, as well as Merlin Park and Portiuncla hospitals, are due to take strike action on Thursday in a row over pay.
Across the country, 10,000 staff - represented by SIPTU - are set to strike, which is likely to cause significant disruption to health services.
The action will involve healthcare assistants, porters, household and catering staff and laboratory aides, and will get underway at 8am on Thursday morning.
The pay dispute follows a job-evaluation process that found the skill levels for HSE support staff had increased significantly in recent years, leading to union claims for pay rises.
Talks held yesterday at the Workplace Relations Commission ended without agreement, and Paul Bell, SIPTU's health division organiser, says Thursday's strike will now go ahead.