Union leaders and politicians have stepped up their campaign to save the Burberry factory in Rhondda.
The union has pledged to continue its campaign
Some 300 jobs will be lost at the Treorchy designer clothing plant, which is set to close by the end of the year.
Campaigners have urged Burberry to reverse the decision and protested outside the factory gates.
In September, Burberry announced a consultation period following a year-long review, which had left "no obvious" alternative to the closure.
But the GMB union said it would campaign to keep the factory open and now plans to target celebrities who wear Burberry, to highlight the issue.
Rhondda AM Leighton Andrews, who joined the factory workers at the demonstration, said closure would be "a major blow to the community".
Mr Andrews said: "There has been a clothing factory in one guise or another in the area since the second world war, so many families in the Rhondda have had members of the families work there over the years."
Burberry took over the Treorchy factory in 1989
Friday's demonstration was the "official launch" of the GMB's campaign to keep the factory open, which would be taken "across Britain", he added.
Sewing machinist Valerie Hughes, from Pentre, said Burberry did not need to close the factory.
"It's making millions," she said.
"We're demonstrating because theyre going to try to get rid of 300 jobs - this is the second time in six months that I'm facing redundancy, I'm very worried."
Claire Millier, a presser, from Treherbert, has worked at the factory for 13 years since leaving college.
She said: "It's awful, nobody knows what's going on, everybody's so worried, it's just terrible - we'll fight this all the way."
Workers from the Visteon car components plant in Swansea, which has also been subject of worries over its future, came to offer their support.
Mr Andrews has written to actor Ioan Gruffudd, who was born in Llwydcoed, near Aberdare, but now lives in Los Angeles, to try to win his support.
"We'll be looking closely at those celebrities associated with Burberry. Lots of celebrities like to wear Burberry, and Ioan Gruffudd is the global face of Burberry," he explained.
Rhondda MP Chris Bryant said he had personal reasons for wanting the factory to stay open, as his father's first job for IBM in the 1960s was to put in the factory's first computing system.
"I want to make sure that those 309 jobs stay in the Rhondda," Mr Bryant said.
"There's not been any complaint about the quality of the work, and it comes down to the simple fact that I want to keep Burberry as a British brand."
Mervyn Burnett, from the GMB union, said Burberry had agreed to delay the 90-day notice period by one month.
"GMB have used this time to gather support from elected representatives and others to maintain production in south Wales.
"We will maintain our campaign to keep the company in south Wales," Mr Burnett said.
A spokesperson for Burberry said: "Should the consultation find that the proposal is implemented, we had always anticipated the site would close around the turn of the year."