Users of disability and community services are set to be hit by rolling strike action in Mayo, Galway, Cork, Kerry and Donegal.
Workers in community and so-called 'section 39' organisations are staging the three day action in a dispute over pay.
Unions say the health and social-care workers in the agencies which are funded by the HSE, are paid considerably less than those employed directly by the HSE and other state bodies.
The focus of today's strikes will be on Co Cork.
Tomorrow's strikes will be at the offices of Ability West in Tuam and Galway city, at Western Care in Belmullet, Ballina and Castlebar in Co Mayo, and at a number of community employment schemes in Co Donegal.
SIPTU's Adrian Kane says the staff haven't had a pay rise in 14 years.