SIPTU, which represents the majority of workers at the Carlow sugar factory, will meet Irish Sugar management next Monday to challenge the rationale behind its closure.
The Greencore-owned plant will cease operations on March 11th, with the loss of more than 300 jobs, in a move which management said will secure the future of the industry.
A meeting of SIPTU shop stewards expressed outrage yesterday at the way Greencore's sugar division had handled the closure.
SIPTU regional secretary, Mr Michael Jennings, said the action had been taken without consultation and seemed to fly in the face of agreements with the union.
"When our members were told of the closure, they were given printed calculations of their entitlements which clearly had been drawn up long before the closure was announced."
"It was done in a very secretive way and before we could get down to our plan to lobby the Government and the Opposition parties to oppose the Fischer reforms in the sugar regime."
Mr Jennings said that SIPTU had a series of meetings set up, the first with Mr Proinsias de Rossa, Labour Party MEP, on February 4th.
Mr Michael Browne, SIPTU's Carlow branch secretary, said the union would brief its members in the plant later today.
Meanwhile, Fine Gael's spokesman on agriculture, Mr Denis Naughten, condemned the closure decision as premature.
"This announcement will have a huge impact on local beet growers and the local economy, not only through the loss of employment but also the major spin off it provided to local services," he said.
"It is important to note that there is not an over-production problem in Ireland, and it is therefore imperative that the Minister for Agriculture retains the current quota available to Irish beet growers."
The president of the ICMSA, Mr Pat O'Rourke, urged the Minister for Agriculture and Food, Ms Coughlan, to exercise her standing as a "golden shareholder" in Greencore, so that "some degree of social perspective and long-term economic planning is brought to bear on the current situation in which the company finds itself".
He said the ICMSA would expect the Minister to exercise her shareholder role, not just with the views of the board or workforce in mind, but also the views and welfare of the farmers, who had been supplying the raw material which kept the whole operation going for 80 years.
Ms Máireád McGuinness, Fine Gael Leinster MEP, said the closure left Ireland with just one sugar processing plant [in Mallow] at a time when the proposed reforms of the European sugar regime had the potential to wipe out the entire industry here.