Over 200 jobs are to be lost in two factories in Tipperary and Monaghan.
The Merriott Radiator plant in Clonmel, Co Tipperary, is to close with the loss of 90 jobs, it has been announced.
Separately, 130 jobs will be lost under a rationalisation plan at Grove Turkeys in Monaghan.
Formerly the Barlo plant, the Merriott factory became part of the Quinn Group in May 2004. It has been in operation since 1967.
Tom O'Driscoll, Grove Turkeys
The Quinn Group said the decision to close follows a review of the business, which found that due to the scale of the operation in Clonmel it has become "particularly difficult to compete in UK and European markets".
Consultation with the the union representing the employees has begun, and redundancies will be phased in by negotiation and agreement over a timescale to be agreed, Quinn Group said.
Clonmel-based Senator Phil Prendergast of the Labour Party said she was shocked that a company with such a long tradition and a "dedicated and excellent workforce" is to close.
"This company was operating in profit due to the hard work, productivity and cooperation of that workforce, but lack of investment in recent times has seen this unwelcome outcome," she said.
At the Grove Turkeys, a rationalisation plan will reduce the core workforce from 200 to 70. The company said the job cuts were in response to intense competition from overseas producers.
"It is with deep regret that we make this decision," said managing director Tom O'Driscoll.
"The very survival of the company is at stake. The fact remains that overseas producers have a phenomenal advantage in terms of costs and we haven't been able to compete with this during the low seasons."
"This is not only a severe blow to the workforce and their families but it will also have a serious impact on 85 farm families north and south of the border who have committed their lives to this industry," Fine Gael TD Seymour Crawford said.
Sinn Féin Cavan-Monaghan TD Caoimhghín Ó Caoláin said: "As the economic slowdown leads to job losses across the country, the Border counties are the least well equipped to deal with the situation."
"Successive governments including the present administration have presided over a development deficit in this region. The glut of development in infrastructure, employment and construction in the east and south of the country has left the Border region in a very vulnerable position and over-reliant on a few industries such as food-processing."
Mr Ó Caoláin called on Minister for Agriculture Mary Coughlan and Minister for Enterprise and Employment Micheál Martin to address the deficit as a matter of urgency before the Grove Turkeys job losses were followed by others.
Today's news came as latest figures from the Central Statistics Office revealed the rate of unemployment rose to 4.9 per cent last month - the highest since December 1999.
It is the latest in a series of job losses since the start of the year. This week 360 workers at pharmaceutical and medical device company Allergan in Arklow, Co Wicklow, were told their jobs would go.
More than 200 jobs were recently lost at Jacob's Fruitfield, in Tallaght, 60 at Britvic in Cork, 400 in the Burlington Hotel, and a further 1,500 are under threat at SR Technics.
Additional reporting: PA