There are renewed fears for the 670 jobs at the Liebherr crane manufacturing plant in Co Kerry.
Around half of the workforce at the operation in Killarney have rejected proposals aimed at resolving a pay dispute.
Last month, the German owned firm said it was re-evaluating its dependence on the plant because of the four year row.
In a statement, SIPTU says it remains available for direct discussions on the matter.
Our News Correspondent Fergal O'Brien reports:
