Chinese e-commerce giant Shein and rival Temu have swapped legal blows at the start of a U.K. trial that’s expected to shine a light on the world of ultra-fast fashion.

Shein accused Temu of “astonishing” levels of copyright infringement, while Temu hit back in court documents, saying its rival waged an “aggressive and relentless battle” using copyright allegations to undermine competition.

Shein sued Temu in 2023 and Temu counter-sued the following year, with the duo seeking damages for alleged losses the other firm caused them. 

The London trial offers a rare window into supply chains of Shein and Temu, founded by billionaires Xu Yangtian and Colin Huang respectively, and how the ultra-fast fashion industry competes for shared suppliers and overlapping production networks. The outcome of the legal battle will influence their supplier relationships as the two budget fashion giants pose a threat to European retailers.

Shein accused Temu of using thousands of photographs from Shein’s website for identical products.

According to Shein’s lawyers, Temu sold items copied or identical clothing items using the same images and seeks to “piggy-back off Shein’s own investment in building up its supply chain and training and up-skilling suppliers.” 

Temu’s lawyers denied the allegations saying merchants, who were responsible for the use of images, had the required consent. 

The case “has nothing at all to do with the protection of any intellectual creativity in photographs, and everything to do with an attempt by the claimant to stifle legitimate competition,” Temu’s lawyer Charlotte May said referring to Shein.

Spokespeople for Shein and Temu didn’t immediately respond to requests for comment.