This morning the Tanaiste, Ms Harney, will appear at the gates of the Seagate plant in Clonmel to show her "solidarity" with the 1,400 workers who learned of their redundancy yesterday.
At a press conference in the town last night, Ms Harney said senior Seagate executives had informed her that the plant had lost $63 million (£43.3 million) since it started operations in Clonmel. They had said that, in hindsight, it had been a bad decision to locate an operation manufacturing this product in Ireland.
"The person who made the decision to locate here no longer works for the company," she said.
Seagate workers said they had been assured by management only two weeks ago that their jobs were secure. But a grim-faced Ms Harney admitted that she learned early in October that the company's Irish operation was under review.
She insisted, however: "I did not know until noon today of this decision (to close)." In October the company had announced the postponement of their proposed location of a second plant in Cork, and at the same time she had become aware "that there might be difficulties" with Clonmel, she said.
She knew that there was pressure on the plant, she said, but she had travelled to the United States for a meeting at Seagate's headquarters and afterwards "we were hopeful that a substantial part of the Clonmel operation could be saved". Last night she cast strong doubt on whether state support would be forthcoming for any further Seagate operation in Ireland.
If the Cork proposal was reactivated, there would have to be "a very critical assessment", she said. "I don't want to see another group of workers in another town having the same experience. This will make us much more cautious about the approach we take.
"I have come here this evening to show solidarity with the workers," she added. "Clearly, the news I heard this morning has shocked me and the Government, and we're going to make every effort, with the IDA and other agencies, to find an alternative factory as soon as possible. Clonmel will be my number one priority now."
The company would be paying back all the grants it had got from the Exchequer. "They have also said they will make the facility available at very reasonable cost," she added. "I believe the plant will be very marketable."
Ms Harney said she would visit the Clonmel plant personally this morning to meet the workers. She acknowledged that the collapse would have "devastating consequences for the region", but stressed that the workforce was both very adaptable and flexible, and that Clonmel was a very positive community.
"Notwithstanding the bad news, we have had two years of employment here for 1,400 people. We have to look at the future, not the past."