Global animal welfare groups have launched a campaign to undermine wool's bid to be a sustainable champion.
They have attacked wool's claim to be the world's premium sustainable fibre.
They claim one out of every two clothing garments made from wool is blended with synthetic fibres "derived from fossil fuels".
Marketers have pushed hard in recent years to separate wool from other fibres with a key battle being fought over green credentials on clothing labels.
In a key battleground of the European Union, wool has even teamed up with cotton, to push their sustainable credentials.
A research document just made public by the Center for Biological Diversity and Collective Fashion Justice "more than half of wool knitwear is blended with synthetic fibres".
The US-based organisation says it tested the fashion catalogues of 13 luxury fashion brands.
READ MORE: Our children are eating more meat, not less
"The analysis found that while wool is often marketed as a natural, sustainable alternative to synthetics, most wool garments are mixed with synthetic materials, contributing to microplastic pollution and worsening the climate crisis," the centre's population and sustainability director Stephanie Feldstein said.
"The fashion industry has tried to pass wool off as a sustainable alternative to synthetics, but that claim quickly unravels when you take a closer look.
"Even 100 per cent wool fibre production leads to deforestation and threatens wildlife. There are real eco-friendly materials out there, but wool isn't one of them," she said.
But the centre's research has been challenged by Australian Wool Innovation.
AWI's program manager (fibre advocacy and eco credentials) Angus Ireland said wool is a natural and renewable raw material which produces durable and long-lived clothing.
Mr Ireland said the fact wool at the end of its life is biodegradable, releasing its nutrients to the soil for use again, is undeniable.
"The argument in this article that wool is 'guilty by association' because manufacturers may incorporate other raw materials in their garments is flawed," he said.
"It is common for garments made from any natural fibre to include some level of synthetic fibre, but this doesn't prevent the positive contribution of natural fibres to the environment through the circular processes of biodegradability and renewability."
The Centre for Biological Diversity and Collective Fashion Justice is campaigning to stop the farming of sheep for wool, among other campaigns directed at farming.
The centre, which is a non-profit organisation funded by donations with links in Australia, claims "wool is a slaughter industry full of hidden cruelty and environmental destruction".
"Wool is not a fibre simply provided by nature - it's a scaled product of modern industrial, chemical, ecological and genetic intervention that's a significant contributor to the climate crisis, land degradation, water use, pollution and biodiversity loss."