The Carlow sugar factory is to close this afternoon with the loss of 190 full-time jobs and 130 seasonal jobs.
The closure of the 80-year-old factory was announced in January, with the company blaming EU reforms expected later this year that will involve cuts in subsidies and quotas.
The company said it would cost €28 million more to upgrade the Carlow facility than to modernise the remaining plant in Mallow.
After the announcement, about 4,000 people demonstrated in Carlow against the move but the company insisted that the decision would not be overturned.
The closure means that Mallow will be the only survivor of the original four factories. Plants in Tuam and Thurles shut down 20 years ago.
Today's closure means that farmers in Leinster will have to have their beet transported by rail to Mallow to be processed.
However, the company warned of further challenges ahead if the surviving factory in Mallow is to compete successfully.