Apple is leading the way in tracing cobalt used in its electronics to ensure the metal has not been mined by children in Democratic Republic of Congo while Microsoft is lagging, Amnesty International said.
Microsoft disagreed with the pressure group's conclusions published on Wednesday.
Congo is by far the world's biggest producer of cobalt, accounting for more than half of global supplies of the metal, a key ingredient in lithium-ion batteries.
Amnesty, however, says about a fifth of the country's cobalt production is mined by hand by informal miners including children, often in dangerous conditions.
Cobalt has shot to prominence in recent months and its price skyrocketed due to expected growth in demand for electric vehicles powered by lithium-ion batteries.
"Companies have a responsibility to prove they are not profiting from the misery of miners working in terrible conditions in the DRC," Amnesty official Seema Joshi said in a statement.
The group ranked 29 companies on how well they were tracking their sources of cobalt since Amnesty released a report in January 2016 warning about human rights abuses linked to cobalt mining in Congo.
"Apple became the first company to publish the names of its cobalt suppliers ... but other electronics brands have made alarmingly little progress," the statement said.
Most cobalt is produced as a by-product of copper or nickel mining, but artisanal miners in southern Congo exploit deposits near the surface that are rich in cobalt.
The biggest buyer of ore from small-scale miners was Congo Dongfang Mining International, a wholly owned subsidiary of Chinese mineral giant Zhejiang Huayou Cobalt Ltd, Amnesty found in its report last year.
Since then, Huayou Cobalt "has taken a number of steps" in line with international standards but "gaps in information remain", Amnesty said.
In March this year, researchers from Amnesty and Congolese group African Resources Watch returned to informal mines and still found adults and children in unsafe conditions, the report said.
Huayou, in a letter to Amnesty, said child labour was a difficult issue caused by poverty, adding that it was working on several initiatives including building schools and providing micro-credit to boost small businesses.
Microsoft was among 26 companies that had failed to disclose details of their suppliers, Amnesty said.
In a letter replying to the Amnesty report, Microsoft said its approach was "holistic" and included work within its supply chain as well as on the ground to address the socioeconomic causes of child labour.
"Despite Amnesty International's assertions, Microsoft has made significant progress on this important issue," it said.
Cobalt prices have spiked 85 percent this year on forecasts that demand will double in the next decade due to surging use of the metal in electric car batteries.
Amnesty said among car makers, BMW had made the most improvements, while Renault and Daimler "performed particularly badly".
Renault said it had set up a working group with its suppliers, which had already shared their systems of controls, their supply-chain policies and details of audits.
The French company had also joined the Responsible Raw Materials Initiative, which expects its first pilot audits by the end of the year, it added in a letter to Amnesty.
Daimler said it was working on identifying the smelters and mines that supplied cobalt to the company.
"Daimler is by no means ignoring its responsibility in terms of human rights due diligence, as your current statement seems to suggest," it told Amnesty.
© Thomson Reuters 2017