This sends a powerful signal to the logging and pulp sectors that market demands are shifting.
The companies, retail and design leaders H&M and Zara/Inditex, developed these new purchasing commitments in partnership with environmental organization Canopy.
The sustainability brand Loomstate, EILEEN FISHER, Quiksilver, and 17 other brands and designers are also backing the 'Fashion Loved by Forest' campaign - an initiative to address the growing impacts of the clothing industry on the world's forests, biodiversity and climate.
"These clothing sector leaders are showing that being stylish doesn't have to cost the earth", said Nicole Rycroft, Canopy's Executive Director.
From forest to tank-top
Canopy research has found that threatened forests are routinely making their way into clothing. Rayon, viscose, modal and other trademarked fabrics are increasingly made from the world's most endangered forests, from the tropical rainforests of Indonesia to the great northern Boreal Forests.
Globally rare forests are cut down, pulped and spun into suit jacket linings, dresses, skirts, t-shirts and tank tops.
The pulp/viscose industry is poised for continued ambitious expansion and poses an increasing risk to threatened forest ecosystems around the world. But the promises made by these brands will help curtail the problem and build solutions.
Last year, an estimated 70 million trees were cut for fabric production, a number projected to double in the next 20 years. The last intact rainforests of Indonesia are falling at an alarming rate and species such as the critically endangered orang utan may vanish within our lifetimes if this trend is not reversed.
The global apparel industry is a $1.2 trillion sector with enormous market and cultural influence.
Style does not have to cost the Earth
"Canopy is excited to see two of the largest brands, both major trendsetters, stepping up to ensure fabrics are no longer sourced from the world's endangered forests", said Rycroft.
"Their efforts will both help them avoid fibre from contentious forest regions and send a powerful signal to the logging and pulp sectors that market demands are shifting."
Henrik Lampa, Environmental Sustainability Manager at H&M, said:"H&M wants to play a strong role in ensuring a future for the planet's ancient and endangered forests. We are fully committed to exploring our supply chain and doing our utmost to avoid these fabrics within the next three years", said
"Working with Canopy, we are excited to take the additional step of encouraging leaders throughout the supply chain to support conservation in endangered forests and use alternative inputs, for example recycled clothing, so our actions create lasting change."