The assembly government has pledged its full support to 900 Bosch workers who will lose their jobs when the company's south Wales plant closes.
The German motor parts company has recommend closure of its Vale of Glamorgan site to its board, transferring work to Hungary in 2011.
It said sales were down at the plant.
Union leaders say the closure is "devastating". Deputy First Minister Ieuan Wyn Jones said staff would be helped to find new jobs or gain skills.
The factory opened in Miskin in 1991 to make alternator products for cars, with the help of £21m in public grants from the Welsh Development Agency, which was subsequently absorbed into the Welsh Assembly Government.
At its peak it employed some 1,500 people.
However, the company warned the workforce in September last year that jobs were at risk unless demand and sales improved.
Announcing a 90-day consultation in October, it warned that it expected a sales decline to continue, slashed by up to 65% in 2010.
Following the review, management spent Thursday informing the workforce of their decision to move out of Wales.
It said it was facing the worst economic downturn for decades, saying that this had "left its mark on the Bosch Group".
In a statement, the firm said consultations are now being extended until February, as unions and staff attempt to thrash out redundancy terms.
Nick Servini, BBC Wales business correspondent
This announcement comes at a time when, ironically, most people felt the worst of the job losses were behind us in this recession.
It should act as a sharp reminder about how difficult any economic recovery will be if a blue chip manufacturer like Bosch is pulling out of Wales next year.
And the shockwaves will be felt in many communities as workers travel to this huge plant from all over south Wales.
The blame game will inevitably begin now. Most people accept that Bosch was in a difficult position as a result of the huge fall in sales.
But critics will claim that the Miskin plant was always vulnerable with investment in the new generation of alternators going to other countries.
Stefan Asenkerschbaumer, president of the Bosch starter motors division, said he "deeply regretted" that a "solution" could not be found for the plant, where he had previously been manager.
"I know first-hand the dedication and commitment of the employees here," he said.
"Therefore, this is for me personally one of the toughest decisions in my career."
The union Unite, which represents much of the workforce at the site, said it had spent the last three months in detailed discussions with the company, in a bid to save the plant.
It said it will hold a mass meeting at the plant on Saturday where it will explain how it intends to support its members.
Unite regional officer David Lewis said the workers are "absolutely devastated".
"Since October last year, Unite has been seeking alternatives to the closure of the site, but the company has not supported our proposals," he said. "This is a terrible blow to 900 workers and their families. We will now vigorously campaign for the best possible deal for the workforce."
Mr Lewis said he understood that the factory would now close in the summer of 2011.
David Lewis of the union, Unite: "Everyone is bitterly disappointed"
"I think everyone is bitterly disappointed that there's not a hope of something being retained," he said.
"The company confirmed that they have a very skilled, a good workforce, but that doesn't take away from the destruction of people's livelihoods and the difficulties for their families.
"So, they are completely and utterly bereft I think of what they can see for the future."
Deputy First Minister Ieuan Wyn Jones said the assembly government was pledging its full support to the workers.
"This is extremely disappointing news and a significant blow to the hard working and highly-skilled employees of Bosch and the wider community," he said.
"We have regularly met with senior representatives of the company, and today I met with them again to press the case for keeping the plant open. Despite our efforts, we deeply regret that Bosch have come to this decision to proceed with the option to phase out production.
Bosch is situated in the M4 corridor in south Wales
"If this decision goes through, we will continue to do everything possible to help those affected, whether it is helping them find new jobs or gain new skills so they can start alternative careers."
Plant director Adam Willmott said move was one of "pure economics" after a feasibility study had concluded the switch to Hungary, where labour costs were 65% of those at the plant, was necessary to gain the benefit of economies of scale.
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