A coalition of 12 civil society groups have warned the European Commission should not rely on a hotly debated method to assess environmental impact when it outlines rules on how brands should substantiate green claims at the end of next month.

In an open letter sent to European lawmakers Monday, organisations including Fashion Revolution, Fair Trade Advocacy Office and the Clean Clothes Campaign said the so-called Product Environmental Footprint Rules currently under development risk giving “a limited and unholistic picture” of impact, and should not feature as a standalone method to underpin product labels in proposed legislation.

The criticism plays into an increasingly heated debate over how fashion’s environmental impact should be measured and disclosed. Critics of the current PEF method argue that the scope and quality of the data used are insufficient and fail to fully capture factors like social impact, toxic chemicals, overproduction, microplastics, and the true impact of synthetic fibres like polyester.

The letter comes just a week after another coalition of natural fibre producers and environmental groups, Make The Label Count, wrote to the European Commission with similar complaints about the PEF method, warning that, “if not done properly, EU textile legislation could give licence to greenwashing.”

The European Commission did not immediately provide comment.

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