Closure of the Seagate plant in Clonmel was "never on the agenda," the Tanaiste and Minister for Enterprise and Employment, Ms Harney, told the Dail.
Downgrading the workforce of 1,400 to 750, or upgrading the facilities, were the options being considered by the company when she spoke to it several times.
"To say we were shocked by the decision is an understatement because this closure was never on the agenda, nor were we ever informed it was," she said.
The Minister, the IDA and Seagate were sharply criticised by opposition deputies, who expressed their shock at the closure. The Minister was also accused of misleading the House when she knew three months ago that the company was reviewing its operations.
Ms Harney expressed her regret that the workers heard the decision before it was to be announced by the company.
She was hopeful that the Government would succeed in finding a replacement industry very soon. There were several projects in the pipelines and the plant "is a modern state-of-the art building and it has a dynamic young workforce."
She would soon be announcing the members of a task force which would look after the needs of the workforce in the way that was done when Packard Electric in Tallaght closed, and find a replacement industry.
She said that when she met senior Seagate executives in California in October they told her they were considering two options for Clonmel. "The first option was to upgrade the facility, to invest more money and produce an upgraded product which would maintain all existing jobs."
The second option was to downgrade the facility and reduce the workforce to 750. They told the Minister that the cost of production in Clonmel was three times higher than in the Far East. Seagate's board was to make a decision on December 8th.
The Fine Gael deputy leader, Mrs Nora Owen, questioned how the Minister could expect Seagate's employees to accept that "such a decision was made overnight".
She did not believe that a company of this scale could make such a decision in a matter of a few days. "It is quite clear from what we now know that the position of the Clonmel plant was under review for three months."
Mrs Owen said it was extraordinary that 24 hours before the announcement staff had been informed that facilities were being upgraded, and were being informed about a wage increase they would be getting over the next two years.
"Minister, you have to take responsibility for allowing people to raise loans to buy houses or cars, to invest in their children's education, to spend money on Christmas shopping for their family and friends, at a time when you personally knew there may not be salaries available to meet these expenditures."
Her party colleague, Mr Hugh Coveney (FG, Cork South-Central) appealed to the Minister not to abandon the possibility of Seagate's Cork plant, given that its products, technology and the competition it faced were very different from those of the Clonmel plant.
Labour's spokesman on employment, Mr Tommy Broughan, said the debacle raised "the most serious questions about the judgment of the IDA and the Minister for Enterprise, Trade and Employment."
He accused the Tanaiste of misleading the Dail on two occasions in October and November. The Tanaiste had said it would not be appropriate to seek a replacement industry for Clonmel after talks with Seagate executives, "yet you knew that Seagate was carrying out a worldwide review of its operations, including Clonmel."
He said the Minister should have warned the Oireachtas and the people of the town.
"You are responsible for the cruel and inhumane way in which this terrible news was given to workers yesterday, and for the failure to forewarn and protect them."
Democratic Left's employment spokesman, Mr Pat Rabbitte, said he did not believe that the Minister could win in this situation. "If the Minister is seen to have been somehow negligent, then she should be held to account.
"But if there is no manifest negligence by the Minister I think that we are probably all wasting our time in pretending that any Minister of an Irish government can prevent a multinational corporation who decides that it's in its own corporate interest to make a decision such as this."
Mr Michael Lowry (Ind, Tipperary North) said, "It seems incredible to me that the IDA was so out of touch that this decision took it by surprise."