One hundred and seventy jobs are to go at Cameron gas and engineering factory in Co Longford.
Workers said they had been told this afternoon that the facility is to close.
In a statement, Cameron Ireland said the severe downturn in the oil and gas industry has had a dramatic impact on the plant.
Willie Quigley of the Unite trade union has called on Minister for Jobs Mary Mitchell O'Connor and her department to intervene.
Speaking on RTÉ's Six One News, he said the union had no indication that the scale of the job losses would have been so large.
The union will be arguing for "something major" to be done in terms of a redundancy settlement, he added.
Mr Quigley said: "We think in the first instance we will be hoping that the minister and his department can intervene to avert this and that the Chamber of Commerce and the commercial end of the county will get behind this to see if anything can be done to avert the magnitude of this and to reduce it by such big numbers.
"If that fails, then obviously the trade union has to support its members and do whatever needs to be done in terms of a settlement package for them," he added.
Longford Chamber of Commerce and Industry has called on the Government to make a retraining fund available for the workers losing their jobs.
Chamber President Derek Scanlon said that the Government has a responsibility to ensure that the IDA puts a focus back on Longford to help in replacing the lost jobs.
In a statement, he added: "In particular the Government needs to ensure that sufficient attention and visits by FDI companies occur.
"According to the IDA own statistics Longford had 2 IDA visits in 2015 while the other counties in the IDA Midlands region had many more – Westmeath with 28; Laois 4 and Offaly 8.
"This highlights the great divide created by the IDA and Central Government."
In a statement, the company said that a severe downturn in the oil and gas industry "has dramatically impacted Cameron Surface equipment and Subsea order intake, leaving many of our plants underutilised".
It said: "It is with great regret that we advised our employees today that potentially manufacturing, assembly and test activities in Longford would cease during 2017.
"We understand the impact of this announcement on our employees and the local community.
"This is only a proposal at this stage and we will be conducting consultation with the unions and employee representatives and make every effort to try and mitigate as much as possible the impact on our employees."
The company said it would maintain a presence in Longford.
"It is anticipated that we will continue to employ approximately 50 of our current employees. This again is subject to consultation," it added.
Uncertainty has surrounded the future of jobs at the engineering and manufacturing plant in Longford since an announcement of potential job losses at its UK sister company, Onesubsea in Leeds.
Staff at Onesubsea were told that up to 600 jobs there are at risk.
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