Clothing retailers that have stopped buying cotton sourced from Xinjiang may still be using forced labour in their supply chains through companies in China that process imported cotton, the US customs agency believes.

The Biden administration has stepped up sanctions and other measures against China over its treatment of the mainly Muslim Uyghur minority in the province of Xinjiang, and in March said that policies such as mass internment and sterilisation constitute genocide and crimes against humanity. China denies the claims.

Globally, companies have come under pressure to ensure Xinjiang is scrubbed from their supply chains, or to ensure Uyghur forced labourers are not being used to make goods.

The US Customs and Border Protection (CBP) agency seized two shipments of cotton shirts belonging to Japanese retailer Uniqlo upon arrival at Los Angeles and Long Beach port in January under regulations designed to prevent goods made with forced labour from entering the country.

The CBP rebuffed appeals by Uniqlo to release the shipments, arguing that the company had not provided enough evidence that major yarn producer Lu Thai Textile Co. Ltd and garment manufacturer Chenfeng (Jiangsu) Apparel Co. Ltd had not used forced labour from Xinjiang to produce the items.

The CBP letters, which have since been removed from the agency’s website, show for the first time the level of proof the US government is demanding from importers to prove that supply chains are free of forced labour in Xinjiang.

The shipments were detained under a withhold release order (WRO) issued in December last year, which allows customs officials to detain shipments containing cotton or cotton products originating from the Xinjiang Production and Construction Corps (XPCC), a Beijing-controlled economic and paramilitary organisation that produces and processes cotton.

Importers subject to an WRO can choose to either ship the goods out of the US, or file a protest asking for their release.

After the shipments were impounded on January 5 and January 11, Uniqlo filed protests showing that the raw cotton originated from seven suppliers in Australia, Brazil and the US.

But the CBP said that regardless of the cotton’s origins, “Uniqlo has not provided substantial evidence to establish that the entities within the XPCC that processed that cotton into the subject goods did so without the use of forced labour”. It did not specify why it suspected the products were at least partly produced by the XPCC or with forced labour.

The CBP listed 15 deficiencies in the retailer’s evidence, including inadequate records from unnamed spinners and fabric weavers and dyers, insufficient detail in garment inspection reports, certificates lacking information such as dates and factory locations and invoices that omitted fabric composition details.

“Although Uniqlo has provided evidence relating to the sale, acquisition, source location, transportation, and delivery of the raw cotton used to produce the subject cotton garments, as exemplified above, it has not provided any probative evidence to establish that their imported cotton garments were not produced in part by forced labour by the XPCC,” the letter says.

In the January 5 letter – which was published on social media by a UK academic and reported by news outlets before being removed from the CBP website – the names of Uniqlo’s suppliers in China are redacted.

But in the January 11 letter, seen by GTR since its removal, the processor of the cotton is identified as Lu Thai, which says it “owns the world’s largest production base of high-grade yarn dyed shirt fabrics” and the garment manufacturer as Chenfeng Apparel.

The CBP said a statement submitted by Lu Thai, which reportedly has a factory in Xinjiang, “does not reflect either the dates of transactions, dates of production, goods produced, quantities, or addresses of manufacturing facilities” and that a purchase order agreement from the company was unsigned and did not include the location of other companies involved in the transaction.

A delivery list from Lu Thai to Chenfeng Apparel “does not reflect the composition or what is being delivered” and the date on it is illegible, the letter says. The CBP also said Uniqlo submitted “unsigned, undated and generally illegible” Chinese customs declarations and illegible purchase contracts.

Lu Thai, which is listed on the Shanghai Stock Exchange, has a cotton-spinning factory in Xinjiang, according to company documents cited in an NBC News investigation last year.

The facility supplies its main base in Zibo, a city in Shandong province, which Uniqlo lists on its website as one of its core fabric mills. It is also a supplier to brands such as Hugo Boss, Esprit and Brooks Brothers, according to NBC.

Lu Thai has also used workers supplied by a Xinjiang local government body which has been described in a 2018 Wall Street Journal report as funnelling of forced labourers into factories.

The same government body also sent at least 300 workers on what it described as three-month training and study courses at Lu Thai’s main factory in Zibo, according to a 2018 report in Chinese state media.

Clothing brands Esprit and Peter Millar have ditched Lu Thai over concerns about forced labour in Xinjiang. Major Norwegian private pension fund KLP said in August 2018 it would not invest in Lu Thai, citing concerns about working conditions unrelated to Xinjiang.

Laura Murphy, a professor at the UK’s Sheffield Hallam University who researches Uyghur forced labour, says Uniqlo should have changed suppliers following the publication of Lu Thai’s links to forced labour.

“Since there is no way for them to do a reliable social audit of a factory that is operating in the shadow of a system of mass internment, they also knew that there was no way to prove that there was no forced labour there. They had significant time to change suppliers, but they did not.”

Murphy, who published one of the CBP letters on social media, tells GTR: “These letters from CBP show us that there are companies that are willing to go to great lengths to continue their relationship with suppliers that are engaged in forced labour programmes and also to obscure those relationships.”

“That Uniqlo used imported cotton as a way to continue their relationship with a company known to be engaged in forced labour and that they were caught doing it tells us that CBP is doing their homework to trace the supply chains of products that are coming into the US.”

Uniqlo did not respond to written questions from GTR. In a statement in response to the publication of the January 11 CBP letter, its parent company Fast Retailing said the documents it provided to the customs agency showed “that there is no evidence of forced labour in our supply chain, and that there should be no problem with importing these products into the United States”.

“The documentation covering the nature and origin of the cotton was accepted by Customs authorities. However, while the CBP has previously given clearance to other goods manufactured through the same processes, the CBP did not give clearance this time.” A Fast Retailing spokesperson separately told news service Nikkei that “there is no direct deal” with the XPCC.

Campaign groups have pressured companies and governments in many countries to remove Xinjiang from clothing supply chains completely, arguing the risk of forced labour is too high.

Attention so far has largely focused on the raw cotton picked and processed in the province, which produces around 87% of China’s raw cotton, according to state media. But China is also a large importer of cotton, buying around 2.1 million tonnes in 2020.

“Based on the reasoning of the prematurely released document from the US government, it appears there is a very, very high standard being imposed” for evidence not only of the origin of raw cotton but also its midstream processing, says Claire Reade, a Washington DC-based lawyer who specialises in international trade.

The number of cases where goods are seized due to suspicions of forced labour in China are growing, Reade, a senior counsel at Arnold & Porter, tells GTR.

“This was really a dormant statute for many years and now it’s cropping up again,” she says. “I think the level of seizures is going to depend on the level of resources that the customs service has and how much bandwidth they have to be catching [shipments], but I think they’re going to be trying hard given the concerns about Xinjiang.”

The CBP did not respond to requests for additional details. The agency told International Trade Today that it deleted the letters permanently from its website because they were published by mistake as Uniqlo had withdrawn its protests.