An MP has called for Burberry to lose its Royal Warrant if it goes ahead with the closure of its Rhondda factory.
Sir Alex Ferguson is the latest celebrity to back the Rhondda staff
Burberry plans to shut the plant in Treorchy in March and move production overseas with the loss of 300 jobs.
In the first Commons debate on Royal Warrants since 1628, Rhondda MP Chris Bryant said they should only go to a UK firm with a "fair employment policy".
Burberry said it was very much a British company that employed 2,000 people in the UK.
Mr Bryant said he objected to the way warrants were issued in a "secretive way". He argued that the Queen should act on the advice of Parliament and this could be achieved through the establishment of a joint committee.
He said Burberry should lose its warrants unless it guaranteed there would be "no slave wages or child labour" when it outsourced polo shirt production from Treorchy.
Advice on granting warrants is provided by the lord chamberlain, who is chairman of the royal household tradesmen's warrants committee.
About 800 firms hold Royal Warrants of Appointment. Burberry, which holds them from the Queen and the Prince of Wales, recently announced a 22% increase in revenue.
But it plans to move production of polo shirts from Treorchy overseas - the company says to Asia or Europe, while the union claims it would be to China.
Mr Bryant argued in a debate in Westminster Hall: "A Royal Warrant is not just a Royal Warrant any more.
"It's been so successful - because of the prestige with which our Royal Family is esteemed around the world - that I think it is also effectively a national seal of approval.
"It's one of the determining factors around the world, in terms of trade, of what counts as Britishness."
However, he said the system was regarded as "secretive and self-perpetuating," with most recommendations for new warrant holders coming from the association.
Plaid Cymru parliamentary leader Elfyn Llwyd gave his support to the campaign. He joined Mr Bryant in condemning the possible environmental impact of transporting Burberry goods from as far as China.
Deputy Commons leader Nigel Griffiths said Parliament did not scrutinise matters within the personal prerogative of the Crown, and he did not think it would be seen as an "immediate priority".
Royal Warrants are granted to people or companies who have regularly supplied goods or services for a minimum of five consecutive years to the Queen, Duke of Edinburgh or Prince of Wales.
A series of celebrity names have backed the Burberry campaign
Burberry has emphasised that it does not intend to abandon the UK and it has offered Welsh staff jobs at its Yorkshire plant.
Mr Bryant's move came the day after Manchester United manager Sir Alex Ferguson became the latest celebrity to lend his name to the high-profile campaign to fight the closure.
Campaigners hope the support of stars including singer Sir Tom Jones and Hollywood actor Ioan Gruffudd - one of the company's "faces" - will make the company think about the impact closing the factory would have on its image.
Robin Croft from Glamorgan University said Sir Alex joining the campaign changed everything as Manchester United was "huge" in Japan.
"With 62 stores in Japan I guess Burberry would be really concerned that this does hit the media over there, and really devalues the brand," he said.
Burberry has announced that it will move its international headquarters in summer 2008 into a 160,000 sq ft building in Victoria, London. About 1,000 staff will move into Horseferry House from five other locations across London.
The Estates Gazette said the new building would cost Burberry £5.3m a year with the first 18 months rent-free.