At least 25,000 people are working as slave labourers in Brazil, according to a new report obtained by the BBC.
By Steve Kingstone
BBC correspondent in Sao Paulo
The study, carried out on behalf of the International Labour Organization, says workers are living in conditions unfit for animals.
The bulk of them are working in the Amazon region, clearing forest so the land can be used for cattle and crops.
The as yet unpublished report says members of the political elite are among the landowners responsible.
In 21st Century Brazil workers are being treated not like animals, but worse than animals - that is the stark finding of this report, commissioned but not yet published by the ILO.
It says forced labour is concentrated in the Amazon, where workers are clearing huge swathes of rainforest to make way for cattle and crops, notably soya.
Many slaves are used to clear Amazonian land for cultivation
The working day lasts from dawn until dusk. Those involved live in hovels; they eat from tin cans previously used to hold pesticides.
Often the labourers are in debt to their employers who hire gunmen to ensure order and prevent escapes.
The report says that in the Amazon state of Para, more than 500 rural workers have been killed over the past 30 years. That is a murder rate 26 times the national average.
Politicians and judges
The report does praise efforts by Brazil's left-wing government to tackle the issue, but it says a culture of impunity persists where politicians and judges are among the landowners responsible for perpetuating slave labour.
A whole series of proposed laws remain unratified by the Brazilian parliament.
Indirectly the ILO is itself also a target in this report for failing to help bring about change.
But an ILO spokesman denied the study was being suppressed.
He said it would be published at a later date as part of a broader international report on slave labour.