BMW, Vauxhall and the Volkswagen Group have been forced to respond to allegations that their supply chains have forged a link to Indian mines reliant on child labour.

The group of manufacturers are launching an investigation into the source of mica – a light reflecting mineral – used in its metallic paints following the results of an investigation into illegal mining carried out by The Guardian newspaper.

Campaigners estimate that up to 20,000 children, aged as young as 10, work in the mines of northern India.

The Guardian has traced mica from three mines in Tisri subdistrict Indian exporters Mohan Mica, Pravin and Mount Hill, customers of a Chinese company, Fujian Kuncai, whose website had listed paint suppliers PPG and Axalta as its customers.

Illegal mines sell mica through local traders who, in turn, sell the mineral to Indian export companies. Tracing the mineral’s origins is challenging.

PPG told the Guardian that it does not discuss its supplier relationships with the press but Axalta did confirmed that it was a customer of Fujian Kuncai.

Both businesses said that they “would not tolerate” any use of child or forced labour.

A spokesman for Fujian Kuncai told the Guardian that it was “shocked” by the investigation’s findings and would carry out its own inquiry, adding: “For us it is totally unacceptable that child labour is present in our supply chain and we will act accordingly.”

Fujian Kuncai’s supplier contract stipulate zero tolerance for the use of child labour and the company has contributed £500,000 to a project aiming to eradicate child labour in mica communities in Jharkhand.

A Volkswagen Group spokesman told AM that the business was now embarking on the “comprehensive task” of determining the facts behind the allegations related to two of its suppliers.

It stated: “It is challenging to differentiate mica from legal and from illegal mines. Like us, our suppliers are taking the alleged issues very serious.

“Child and forced labour are prohibited by our sustainability standards and are not tolerated by the Volkswagen Group.”

A Vauxhall statement said: “GM expects our suppliers to be fair, humane and lawful employers, and to enforce similar requirements from their sub-suppliers.

These expectations are outlined in GM’s standard purchase contract terms and conditions, which reinforce our zero-tolerance policy against the use of child labour, abusive treatment of employees or corrupt business practices in the supply of goods and services to GM.

“GM will conduct a full investigation of these suppliers regarding the allegations.”

A statement issued by BMW said: “Our supply chain response team is investigating your claim. Initial findings suggest that two of our suppliers may indeed obtain materials indirectly from Fujian Kuncai Fine Chemicals Co. Ltd.

“In accordance with our guidelines, we have asked these two suppliers to respond to these allegations.

“The BMW Group does not tolerate child labour in its supply chain. If the allegations are substantiated, we will do everything to ensure that the company involved is no longer part of our supply chain in the future.”