240 jobs are set to be lost at the the medical manufacturing plant Roche in Co Clare.
Employees were informed of the decision to sell up earlier today.
Roche Holding AG had been based in Clarecastle since 1974.
A spokesperson has said that the company is committed to working with Minister for Jobs, Enterprise and Innovation, Richard Bruton, and the IDA to seek a buyer for the site.
Roche Holding AG plans to exit four manufacturing sites and pare some jobs in a restructuring programme that will cost about €1.48bn ($1.6bn) over the next five years.
Around 1,200 employee positions will be affected by the exit, the company said in a statement today.
The firm plans to look to divest the sites in Ireland, Spain, Italy and the US to curb job losses.
Departure of Roche Holding AG 'very big blow' - SIPTU
The union representing nearly half of the workers at Roche has said the news was a very big blow, a huge shock and came as a bolt out of the blue as they had no prior warning.
SIPTU organiser, Alan O'Leary, said Roche was a very important multi-national in the area and the jobs were high quality and well paid.
SIPTU represents around 100 of the 240 workers in process operations and laboratory technician roles.
He said they did not know when Roche plans to leave and that the union will work with the IDA to try and secure the jobs by selling the site to another company.
Clare Fianna Fáil TD Timmy Dooley has said the announcement by Roche Ireland is a "devastating bolt out of the blue".
He said: "A huge effort is needed now from the Government to work on finding an appropriate buyer for the plant and work on saving these jobs.
"The immediate shock for the workers will quickly turn to concern for their future livelihoods and the Government needs to do everything it can to respond quickly and comprehensively to this announcement.
"Sadly this announcement highlights a weakness of the regional economy. Today we had another glossy PR driven announcement by the Government with 'Enterprise 2025'.
“This country has serious cost issues, especially in energy, waste costs and legal costs. We have been highlighting this for some time and this has even been highlighted internationally but the government is merely burying their heads in the sand instead of tackling these issues in order to protect existing jobs and future investment opportunities," he added.
Clarecastle Fine Gael TD Joe Carey has said that every effort will be made to support the workers of Roche and to secure an alternative investor for the.
"My thoughts are very much with the workers of Roche and their families at this difficult and uncertain time. I know many of the workforce personally as well as their extended families.
"The announcement by Roche that it is planning to exit the site and market it to alternative investors has come as a shock to everyone in Clarecastle. The plant has made such a huge contribution to Clarecastle, County Clare and the entire Mid-West Region, for the past 40 years.
"I met with Minister Richard Bruton this evening, following this announcement, and he gave me an assurance that every effort will be made to support Roche and its workers in finding an alternative investor,” Mr Carey said.
“The State enterprise agencies have a strong track record in finding alternative investors for plants in similar positions and in particular where there is a long lead-in time. Roche has confirmed they are not planning to exit the site for three years.
"I am committed to doing everything in my power, as well as working alongside Minister Bruton, as well as the IDA, to secure a buyer for the site," he added.
