Bord na Móna workers are to be balloted on industrial action later this month over the refusal of management to pay a 3.5% pay increase.
SIPTU says the workers are due the rise under the Towards 2016 transitional agreement.
In a statement, SIPTU said the workers had been left with no choice but to ballot the workers.
It said the Labour Court ruled in favour of the Bord na Móna workers' pay claim.
SIPTU Organiser and Secretary of the Bord na Móna Oliver McDonagh said: "Management has consistently refused to honour the spirit of the Labour Court recommendation.
"Bord na Móna workers have shown great patience and dignity in dealing with this intransigence by the management of a consistently profitable organisation."
