SIPTU wants to know if social protection payments for Retained Fire Fighters are being deliberately blocked.
The union has written to the Social Protection Minister seeking clarification as the dispute escalates.
SIPTU says it's receiving reports from across the country that Retained Fire Fighters are having their payments refused because of the strike.
The union is accusing the Government of trying to break the dispute by using them as a deterrent to other public service workers who might fight back against poor pay and conditions.
Its letter to Minister Humphreys, highlights the fact these payments are a vital lifeline to many Retained Fire Fighters who do not have second jobs.
Around one third of fire fighters are supported by social protection payments.
SIPTU says withholding these payments from vulnerable families is despicable.
