The food company Nestle has been accused of failing to carry out checks on child labour and other abuses in part of its cocoa supply chain.
A report by an independent auditor, the Fair Labor Association (FLA), says it found "multiple serious violations" of the company's own supplier code.
The code includes clauses on child labour, safety and working hours.
Cocoa is the raw product that makes chocolate in a global industry worth more than $90bn (£58bn) a year.
Earlier reports found that 1.8 million children in West Africa are at risk of abuse through dangerous child labour.
After increasing pressure, Nestle, which is the world's biggest food company, commissioned the FLA to map its cocoa supply chain in the Ivory Coast from where almost half the world's cocoa comes.
FLA investigators tracked the journey of cocoa from the poorest and most remote villages to the exporters that sold directly to Nestle.
They found that while Nestle insisted their primary suppliers - mostly big multi-nationals - agree to their code, it often went no further, despite Nestle knowing the supply chain involved many other stages.
"Now that its supply chain has been mapped," says FLA President Auret van Heerden, "Nestle will be held accountable.
"For too long child labour in cocoa production has been everybody's problem and therefore nobody's responsibility.
"Nestle is taking direct responsibility for decreasing the risks."
The report also found rampant injuries, mainly with machetes that slice into the children's legs as they harvest the cocoa pods, as well as both adults and children working long hours without pay.
There has been evidence of child labour on the Ivory Coast cocoa farms for many years.
In 2001, under pressure from the US congress, Nestle and other major chocolate companies signed an agreement to end the problem - but little was achieved.
The FLA says this is the first time a multi-national chocolate producer has allowed its procurement system to be completely traced and assessed.
It believes the flaws it uncovered apply to all the big chocolate companies.
They say they are studying the findings.
Nestle has now laid out a detailed plan to try to solve the problem.
"The use of child labour in our cocoa supply chain goes against everything we stand for," says Nestle's Executive Vice-President for Operations Jose Lopez.
"No company sourcing cocoa from the Ivory Coast can guarantee that it doesn't happen, but we can say that tackling child labour is a top priority for our company."
For more than 10 years, Ivory Coast has suffered civil war and unrest, much of which activists blame on the fight between rival groups for the tens of millions of dollars earned from cocoa.
The new government that came to power last year has introduced initiatives against child labour and exploitation.
Nestle and the FLA say that if the problem is to be totally eradicated the role of government will be critical.