Users of disability and community services are set to be hit by rolling strike action in Cork, Kerry, Galway, Mayo 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.
SIPTU's Adrian Kane says the staff haven't had a pay rise in 14 years.
"The members that we represent across Section 39 employment and the broader community and care sector haven't received a pay rise since 2008.
"Up until 2008 most of these workers would have had their pay negotiated and pay increases resolved at national level, but since 2008 that hasn't happened."
