Workers at the Burberry factory in south Wales have decided to fight closure plans after a mass meeting.
Burberry took over the Treorchy factory in 1989
Mervin Burnett, of the GMB union, said shock had turned to anger and they are to write to the firm asking it to withdraw the 300 redundancy notices.
The union wants to examine the firm's financial position and consider ways to save the plant at Treorchy, Rhondda.
Burberry will talk to the assembly government but it looks set to move production to Asia or South America.
Burberry said the plant was not "commercially viable", but the company would not abandon the UK when the Rhondda plant closes in December.
The GMB union said it is appalled by the decision, claiming Wales had now lost 46,000 manufacturing jobs since 1994.
Enterprise Minister Andrew Davies said he would be talking to Burberry's managing director to make the case for the firm retaining its Rhonnda operation.
He said the closure was "a bolt from the blue" with no indication that they were planning an announcement.
"We certainly want to find out why they are doing this to see if there's anything we can do as a government to change their minds," Mr Davies said.
Rhondda MP Chris Bryant said he felt angered and betrayed by the news that the plant making polo shirts was to close.
He said senior managers had guaranteed to consult him before they considered closure and broke their promise.
Mr Bryant told BBC Wales he had met senior management two years ago, and they had guaranteed then they were not thinking about closing the plant.
"If they were even going to be thinking about going down that line, they [said they] would get in touch with me first, so that if there was a package we could put in from the Welsh assembly to help them stay here that would be possible, and they've not stood by that promise," he said.
However, Mr Bryant said he thought there was still a chance the factory could be saved, and he and Rhondda AM Leighton Andrews met the managing director on Wednesday to discuss the situation.
The company said the closure plan follows a year-long review of its supply chain and manufacturing process, leaving managers with "no obvious alternative other than to propose the closure of the factory".
Production will go overseas, where costs are lower. The firm has not said specifically where, but it will be either Asia or South America.
It stressed the proposed closure was a one-off and the company would not abandon the UK, and there were no cuts planned at other sites.
Local councillor Robert Bevan said: "This is a bitter economic blow to the Rhondda Fawr and the county as a whole."
The factory at Treorchy has been producing clothes since 1939 but it was only taken over by Burberry in 1989.