Members of the Fórsa trade union employed by Enable Ireland in Cork and Kerry are to take strike action on Friday 23 September.
The union said it has served notice of the industrial action following a ballot of its members.
Unions have already announced a series of one-day strikes in community and voluntary sector agencies in Galway, Mayo, Cork and Donegal on Wednesday 21 September and Thursday 22 September as part of a campaign demanding improved funding and pay for the sector.
The agencies affected include the Irish Wheelchair Association in Cork, St Josephs Foundation, EmployAbility Cork, Western Care, Ability West and selected community employment (CE) schemes in Donegal.
Unions say that health and social care professionals employed in agencies funded by the Health Service Executive are paid significantly less than equivalent workers employed directly by the HSE and other State bodies.
'Section 39' organisations are contracted to provide services on behalf of the HSE for a funding grant in accordance with Section 39 of the Health Act 2004.
The Department of Health says that because such organisations are privately owned, setting pay rates for their staff is not a matter for the Government.
"This is a huge step for the staff at Enable Ireland, which include health and social care professionals, speech and language therapists, occupational therapists, psychologists, physiotherapists, social workers, support workers, bus drivers and administrative staff," said Fórsa official Eddie Walsh.
"Government is failing to grasp the link between its chronic under-funding of the services we're talking about and the failure to meet the HSE's recruitment targets in disability services like those provided by Enable Ireland," he said.
