The legal complaint on behalf of 14 families from Congo was filed on Sunday by International Rights Advocates, a U.S.-based human rights non-profit, against Tesla Inc, Apple Inc, Alphabet Inc, Microsoft Corp and Dell Technologies Inc..

The companies were part of a system of forced labor that the families claimed led to the death and serious injury of their children, it said.

It marked the first time the tech industry jointly has faced legal action over the source of its cobalt.

Images in the court documents, filed in U.S. District Court in Washington D.C., showed children with disfigured or missing limbs.

Six of the 14 children in the case were killed in tunnel collapses, and the others suffered life-altering injuries, including paralysis, it said.

“These companies – the richest companies in the world, these fancy gadget-making companies – have allowed children to be maimed and killed to get their cheap cobalt,” Terrence Collingsworth, an attorney representing the families, told the Thomson Reuters Foundation.

Cobalt is essential in making rechargeable lithium batteries used in millions of products sold by the tech industry.

More than half of the world’s cobalt is produced in Congo.

Global demand for the metal is expected to increase at 7% to 13% annually over the next decade, according to a 2018 study by the European Commission.

The lawsuit said the children, some as young as 6 years old, were forced by their families’ extreme poverty to leave school and work in cobalt mining owned by the British mining company Glencore. Glencore has previously been accused of using child labor.

Some children were paid as little as $1.50 per day, working 6 days a week, it said.

In response to a request for comment, Dell said in an email that it has “never knowingly sourced operations” using child labor and has launched an investigation into the allegations.

A spokesperson for Glencore said: “Glencore notes the allegations contained in a U.S. lawsuit filed on 15th December 2019.

“Glencore’s production of cobalt in the DRC is a by-product of our industrial copper production. Glencore’s operations in the DRC do not purchase or process any artisanally mined ore.

“Glencore does not tolerate any form of child, forced, or compulsory labour.”

Tesla, Apple, Google, Microsoft did not immediately respond for comment.

The legal complaint argued that the companies all have the ability to overhaul their cobalt supply chains to ensure safer conditions.

“I’ve never encountered or documented a more severe asymmetry in the allocation of income between the top of the supply chain and the bottom,” said Siddharth Kara, a researcher on modern slavery who is an expert witness in the case.

“It’s that disconnect that makes this perhaps the worst injustice of slavery and child exploitation that I’ve seen in my two decades research,” Kara said.

More than 40 million people have been estimated to be captive in modern slavery, which includes forced labor and forced marriage, according to Walk Free and the International Labour Organization. (Reporting by Matthew Lavietes; Editing by Ellen Wulfhorst and Tom Finn.