Over 350 lay-offs at three separate companies - two of which are among Ireland's most venerable - has been described as "shocking news" by Tánaiste, Ms Harney.
Tayto snack foods this afternoon announced 179 redundancies involving the closure of its Terenure operation with loss of 164 jobs; and 15 lay-offs at its Coolock plant.
Earlier today, Guinness announced 135 lay-offs amid strenuously denied speculation that it was considering closing the world's most famous brewery, St James's Gate.
Galway firm Oran Precast also announced it was shedding 40 jobs, meaning 354 people have been told their services are no longer required today.
Ms Harney, who is Minister for Enterprise, Trade and Employment said: "These developments clearly underline the challenge that we face in maintaining competitiveness". But she said she was "confident that Ireland was better placed than most of its competitors to withstand the effects of what is clearly a global phenomenon".
However Labour spokesman Brendan Howlin said: "It is clear that we are now facing the most serious jobs situation for many years."
The Tánaiste promised those laid off the "full resources" of State agencies being made available to help them find alternative employment.
Mr Howlin said the job losses marked the end of a "particularly bleak week on the jobs front ... coming on top of last week's live register showing the biggest monthly increase for 19 years".
Tayto announced the redundancies late this afternoon as part of a restructuring plan that will see them invest €5 million over three years in its crisp plant at Coolock. It also announced it was outsourcing production of its snack food range to the Irish company Largo Foods.
Managing Director of Tayto, Mr John Keogh, said: "There were a number of options we had to address as a management team. In assessing these, it became evident to us that outsourcing production of this product range to a third party was the best decision for Tayto and our employees as a whole."
The news followed the announcement by Guinness that 135 workers were to be laid off on both sides of the border in administration, sales and marketing.
Guinness, the brewing subsidiary of the multinational food and drinks company, Diageo, cited a "worsening business environment" as the reason for the cuts. It said it expected the alcohol drinks market in Ireland to be down 5 per cent this year.
One hundred people are to lose their jobs in the Republic, with a further 29 transferring to other parts of the organisation.
The company in Northern Ireland will reduce its workforce by 35, with a further 10 transferring to other Diageo operations there.
It said: "The newly structured organisation aims to ensure a better allocation of resources to areas of greatest potential for profitable growth and also involves a simpler structure which will lower costs and ensure quicker and more effective decision-making".
The cuts come amid growing speculation that Diageo is planning to close the famous St James's Gate brewery in Dublin on the grounds that it is uneconomical.
Meanwhile in Galway, construction company Oran Precast said it would cut 40 people from 110-strong workforce. It blamed rising costs and a fall-off in demand but expected to re-employ the workers when the market recovers.
The Oranmore-based company fined €500,000 last week for breaches of the health and safety laws following the death of an employee on a building site in 2001.