Double Oscar winner Emma Thompson has become the latest celebrity to support workers at the threatened Burberry clothing factory in the Rhondda.
Emma Thompson is the latest star to back Burberry factory workers
The star of Sense and Sensibility and Howard's End joins fellow actors Rhys Ifans, Ioan Gruffudd and opera star Bryn Terfel in a high-profile campaign.
Burberry has been consulting on plans to shut the Treorchy plant in March with the loss of 300 jobs.
It said it had to make sure every part of its business was effective.
In September the company announced it was looking at proposals to move production abroad, saying the factory was not "commercially viable".
But it has since said it does not intend to abandon the UK and has offered Welsh staff work at its site in Yorkshire.
In a statement, Ms Thompson warned that Burberry would appear "inauthentic" if it exported jobs abroad.
"At a time when it behoves all businesses to set their ethics in order and put honourable practice above profit, I call upon Burberry to reconsider their decision to move out of the Rhondda valley," Ms Thompson said.
"When I buy clothes, I always check to see where they are made.
"When an item that is so clearly branded as British (to the core) is ''Made in China', I'm afraid that I often put that article straight back, suspecting corporate greed and unacceptably low wage packets for the producers of that article.
"Burberry should not make this move - it will brand itself as greedy, unethical and - perhaps most importantly for the profile of the company - inauthentic."
Ms Thompson said by staying in Wales, the company would "retain its code of decency and high standards."
She added: "Anything else is a betrayal of the workforce and a bastardisation of the brand."
Burberry workers have taken their protest to London
Ms Thompson, the only person to have won Oscars for both acting (Howard's End) and writing (Sense and Sensibility), joined the campaign following a request by Euro MP Glenys Kinnock.
The workers from the Treorchy factory currently make up a third of Burberry's 900-strong manufacturing workforce in Britain.
Burberry's company secretary Michael Mahoney said the firm's workforce in Britain had grown by a third in recent years.
"This is due to the success of the business and that we manage the business to ensure continued long term success," he told the BBC.
"The issue is making sure we make every part of the business as effective as possible.
"We're concerned to continue the great success of the last few years - that success enable the company to grow. A company that grows is able to employ people."
A spokesman for Burberry said: "We are proud to retain a strong manufacturing
capability in the UK. We make our iconic trench coats in Yorkshire and have no
plans to change this."
Workers picketed Burberry's flagship stores in New Bond Street and Regent Street in October.
Managers are also likely to be summoned to justify its closure before a committee of Welsh MPs.