Technology giants Apple, Samsung and Sony have been accused of failing to ensure the materials used in their products do not come from mines that exploit child labor.
Amnesty International and African Resources Watch (Afrewatch) have all accused the companies of lax oversight of their supplies of cobalt from mines in Democratic Republic of Congo.
Cobalt is used in rechargeable batteries found in many laptops, mobile phones and electric vehicles.
A report produced earlier this year by the campaign groups says consumer products sold around the world could contain traces of the metal from informal Congolese mines, without technology companies knowing.
In response, Apple said it had a zero tolerance policy towards child labor and was evaluating ways to improve its identification of labor and environmental risks.
Samsung SDI said it conducted written evaluations and on-site inspections of all suppliers to certify compliance with human rights, labor, ethics, environment and health standards.
The report identified children as young as 12-years-old were working underground digging up the metal in the mine.
Once processed, the cobalt is sold to battery component manufacturers in China and South Korea, which supply the multinationals.
Huayou Cobalt is the largest cobalt chemicals producer in China and sold almost $235 million of the metal in 2013, according to the report.
Once smelted, the cobalt is exported to China before being sold to battery manufacturers who claim to supply top-end electronics companies including Apple, Samsung, Sony and 13 others, the report said.
Congo’s supply of the metals such as tantalum, tin, tungsten and gold has been under scrutiny since 2010, when laws in the United States required US-listed companies to ensure their supply chain was free from these so-called ‘conflict minerals’.
But cobalt has received scant regulatory attention, although strifetorn Congo is the source of more than half of global supply.