According to a new investigation performed by Amnesty International, Apple is one of several technology companies using cobalt mined by child labor in their lithium-ion batteries. The report claims that Apple, Sony, Samsung, and Microsoft are all using the cobalt mined by child labor, as are electric car makes like Volkswagen and Daimler.

There are a handful of steps before the cobalt actually gets to an iPhone, however. Traders first purchase the mined cobalt from small producers, then sell it to Congo Dongfang Mining, which is a subsidiary of Zhejiang Huayou Cobalt Ltd, a Chinese mineral retailer. Battery manufacturers are next to acquire the cobalt, using it to produce the lithium-ion batteries found in smartphones like the iPhone.

Amnesty International conducted interviews with 87 current and former cobalt miners, 17 of which were children. The children told the organization that they worked 12 hours a day in the mines, carrying heavy loads and earning between one and two dollars per day. One 14-year-old boy stated that he would work 24 hour shifts in the tunnels. There are an estimated 40,000 children working in mines throughout the Democratic Republic of the Congo, some as young as seven.

Regarding the Amnesty International report, Apple issued a statement to the BBC. The company reaffirmed that it has a zero-tolerance policy when it comes to the use of child labor in its supply chain. Apple says it is currently investigating the claims against its cobalt supplier.

“Underage labour is never tolerated in our supply chain and we are proud to have led the industry in pioneering new safeguards. We are currently evaluating dozens of different materials, including cobalt, in order to identify labour and environmental risks as well as opportunities for Apple to bring about effective, scalable and sustainable change.”

When a supplier is found to be violating child labor laws, Apple forces it to perform the following tasks:

fund the worker’s safe return home

finance the worker’s education at a school chosen by the worker or his/her family

continue to pay the worker’s wages

offer him or her a job when he or she reaches legal age to work.

Every year Apple releases a Supplier Responsibility Progress Report that discloses information discovered in audits of its suppliers around the world. Last year, the company dropped four smelters from its supply chain after they refused a conflict-free audit. In 2014, Apple was put under fire for a BBC documentary that claimed to show the negative working environment of Apple’s supply chain. Following the accusations, Tim Cook said he was “deeply offended” by the allegations and that Apple is constantly working to improve working conditions.

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