The future of more than 200 jobs at the Roche Ireland plant in Co Clare hung in the balance last night after SIPTU workers voted to continue their strike.
The workers' decision follows a management ultimatum that it would transfer Roche's manufacturing operations out of the country if there was not an immediate return to work.
Production halted at the Swiss-owned pharmaceutical plant in Clarecastle more than five weeks ago after SIPTU issued official strike notice, claiming that the company had ignored the last-in-first-out principle when making nine workers redundant.
Earlier this week the management indicated that it was willing to accept a Labour Court recommendation aimed at ending the dispute, which offered increased severance packages to the nine workers.
The Labour Court's proposals were rejected by SIPTU members at a 3 1/2-hour meeting yesterday.
This followed rejection of earlier Labour Court proposals by SIPTU in February.
A union spokeswoman said after the meeting yesterday: "We had full discussions on the proposals the company had put to us arising from the dispute, which the company was saying to us was their final position.
"The company was felt by the general meeting to be extremely inflexible in its response to the Labour Court document, and as a result there was not a willingness by employees to return to work on the basis of those proposals, so the dispute continues."
In its ultimatum to the 75 workers on strike, the company said the production of its main product, dl/acid, would remain at its plant in Boulder, Colorado, for the immediate future and possibly permanently.
The company said the transfer of other products to alternative manufacturing locations would begin immediately if there was no immediate vote to return to work.
The managing director, Mr Bob Costello, said: "Roche believes it has acted reasonably, responsibly and generously throughout this dispute, particularly in accommodating both recommendations of the Labour Court.
"A vote to continue the strike will not result in any further moves or offers by the company."