SIPTU members employed in community schemes in seven additional counties have voted to join strike action next week.
Workers at the Irish Wheelchair Association will hold a one-day work stoppage on Tuesday as part of a pay dispute.
On Wednesday, SIPTU members employed in a number of community organisations in counties Waterford and Galway will go on strike.
They will now be joined by workers from schemes in counties Meath, Kilkenny, Kildare, Clare, Westmeath, Louth and Donegal.
"The worsening cost of living crisis means that these workers feel they now have no option but to take a stand and demand their first pay rise in 14 years," said SIPTU Public Administration and Community Division Organiser Adrian Kane.
'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 these organisations are privately owned, setting pay rates for their staff is not a matter for the Government.
The HSE said that the Irish Wheelchair Association received income of €50.7m in 2021, up from €46.9m in 2020.
"We are working with our colleagues nationwide to reduce the impact of this action," the HSE said in a statement.