Apple, Samsung and Sony are among major companies that are not doing their part to ensure child labor is not being used in the production of their products, said Amnesty International, in a report released Tuesday.
The tech giants have failed to conduct enough checks to make sure children are not being used to mine the cobalt used for lithium-ion batteries, alleges the human-rights organization.
In its report, "Exposed: Child labour behind smart phone and electric car batteries," on cobalt mining in the Democratic Republic of the Congo, Amnesty International found children as young as seven mainly working in mines.
The report documents how traders buy cobalt from areas where child labor is rife and sell it to Congo Dongfang Mining (CDM), a wholly-owned subsidiary of Chinese mineral giant Zhejiang Huayou Cobalt Ltd (Huayou Cobalt).
Amnesty International's nine-month investigation describes how Huayou Cobalt and its subsidiary CDM process the cobalt before selling it to three battery component manufacturers in China and South Korea.
In turn, they sell to battery makers who claim to supply technology and car companies, including Apple, Microsoft, Samsung, Sony, Daimler and Volkswagen.
Dozens of children told Amnesty International they worked for up to 12 hours a day in the mines, carrying heavy loads to earn between one and two dollars a day.
"This is equatorial Africa and these children are facing very tough conditions, breaking rocks, exposed to cobalt dust, with no face mask, hats or gloves, no protective equipment. All the people we spoke to have complained about having health problems," said Mark Dummett, Amnesty International business and human rights researcher, in a telephone interview with CNBC.
All the companies named in the Amnesty report said they had a zero-tolerance policy toward child labor, and released statements to Amnesty International denying the knowledge of use of children to manufacture their batteries.
"There is a problem in the lack of transparency in supply chains," said Dummett, to CNBC. "We ask them [the companies] about whether they knew if the cobalt came from the DRC and none of the companies said they had in place adequate systems to trace this."
"We think that in this day and age, consumers have an expectation for companies to know and show where the raw materials come [from]," added Dummett.
In a statement, Volkswagen said, "To our best knowledge, the cobalt in our batteries does not originate from the DRC."
Sony said in a statement: "We take this issue seriously and have been conducting a fact-finding process. So far, we could not find obvious results that our products contain the cobalt originated from Katanga in the DRC."
Apple wrote, "Of more than 1.6 million workers covered in 633 audits in 2014, our auditors uncovered 16 cases of underage labor and all were successfully addressed. We take any concerns seriously and investigate every allegation."
No regulation of the global cobalt market is in place. Cobalt does not fall under existing "conflict minerals" rules in the U.S., which covers gold and other minerals mined in the DRC, according to Amnesty International.
"Children and miners are living in extremely difficult conditions and companies should help them… [the named companies] need to be part of the solution and can't just wash their hands of the problem," said Dummett, to CNBC.
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