It is a uniquely Scottish art form practised for nearly 400 years but now handmade Fair Isle knitwear is facing a growing threat from cheap foreign machine-made imitators.

Pieces made in Italy and the Far East are being created at a fraction of the cost of the traditional woollen wear, which can take up to 100 hours of patient expertise to complete.

Now a network of concerned women, some of whom have been knitting since the age of four, have linked up under the Fairtrade ethical shopping label with an Edinburgh-based company which is promoting the genuine article in the US.

The Fair Isle Knitting Project has just started a tour of commercial fairs in 15 cities across America including New York, Washington DC, Baltimore, Philadelphia, Boston and Chicago.

Teresa Fritschi, the American-born managing director of Thistle and Broom, is promoting the work using a Fairtrade model in an effort to retain the integrity of the product.

"Today, what the consumer is generally buying is a Fair Isle style knock-off that's machine knit.

"To the uneducated Fair Isle is simply a style of knitting, but this is one of Scotland's most unique pieces of intellectual property.

"The crime of it is that these talented women were still being paid about 50 pence an hour until we launched our Fair Isle Knitting Project."

Using the Fairtrade movement as a business model, two-thirds of the retail price goes directly back into the knitters' bank accounts.

Among those to join the group is Rosabell Halcrow, 77, who has lived all her life on Burra Isle in Shetland and has been knitting since she was 12. She said: "It's a great boost for Shetland hand knitting."

Through the group Mrs Halcrow was reunited with an old friend, Agnes Bowie, who she had not spoken to for 50 years since they both worked together as herring girls.

Mrs Bowie, originally from Whalsay but now living in Lochinver, Sutherland, has been knitting since she was four and is about to turn 78. She said: "I've only made one jumper for the project so far so I am very much a beginner.

"I was more or less doing it for family and friends, but I did some for the Romanian children, through the charity shop, so there was something new for them to wear that wasn't just cast-offs.

"However, it wasn't really worthwhile knitting to sell because you didn't get enough for it. The wool is so expensive to buy. I never dreamed it would ever be sold in America. It feels good, and both Rosabell and I are on the net."

The garments range in price from around £20 for a pair of gloves to more than £300 for a sweater. While the Fair Isle industry that sells locally works well under a co-operative, the US knitting project is designed to give the women a share in the market being exploited by international imitators.

Louise Irvine, of islands-based Shetland Knitwear, welcomed the move. She said: "Their prices are considerably higher than ours. In a way it is giving the market a higher profile, but we couldn't possibly follow or we wouldn't sell anything.

"We sell on Shetland and online, but on Shetland most of the shops tend to sell at a lower price than the retail price in order to make it almost like a reward for people when they come here on holiday. Because we do that there is no way we can pay our knitters more. Our knitters are well paid as far as Shetland prices go because we are a co-operative and we are non-profit making so that it is the knitters that get the money.

"It is a totally different market. They are raising the profile of Shetland knitwear and it can't do any harm at all. Our knitters would have to knit a lot more to make the same money."

Ms Fritschi added: "The women are approaching me as a result of an advert I put in the Shetland Times in February and also by word of mouth as it is expanding.

"Most have not sold their products commercially because they were not being paid enough to do it.

"They would make them for friends and family and give as wedding or birthday presents but they have said they wouldn't have otherwise considered selling them commercially."

Anne Macpherson, director of the Celebration of Celts event which launched the US tour in San Francisco, said: "In an attempt to preserve this piece of Scotland's heritage Thistle and Broom has set upon a path to educate the public about this art form. We share their commitment to preserving the unique cultural heritage of Scotland."