More than 4,000 slaves were freed by the Brazilian authorities last year, according to new government figures. But campaigners fear hundreds of thousands more still live and work in near-slavery.
The Brazilian employment ministry said its officials raided 183 farms, the highest number since SWAT-style teams were introduced 10 years ago. In total 4,133 workers were freed, with 7.4 million reals (US$3.2 million) paid to victims, the ministry said.
"What we know about is the tip of the iceberg," said Father Ricardo Rezende, an anti-slavery campaigner and author of Stepping Out of the Shadow: Slavery for Debt in Contemporary Brazil, the first study of modern-day slavery in Brazil.
Although slavery was officially abolished in Brazil in 1889, Rezende said the estimate of just 25,000 could be way off the mark.
"The real figure could be 250,000," he said.
Brazil's modern-day slave trade began to boom again during the 1964 military dictatorship.
Following the creation of Sudam, a regional development agency which opened up industries in the Amazon region in 1966, business people and cattle ranchers flocked to the rainforests to make money.
The landowners employed middlemen, known as gatos, who found unemployed workers in Brazil's impoverished rural communities, often in northeastern Minas Gerais.
"The gato arrives in a community and says he can get legal work in a certain place," Rezende said.
"They say the person will be able to send money home to their family ... [but] when they arrive they discover they owe money for the transport and the food. The first imprisonment is that of the soul," he added.
"Often a worker will have the false sense that he is in the wrong [if he flees]," Rezende said.
Neide de Oliveira was the first prosecutor in Brazil to secure a conviction against a farmer for using slave labour in 1998.
She said landowners manipulate workers, knowing that slavery is, for many, a more attractive proposition than unemployment.
"I once interviewed a worker with malaria, and the farmer had given him a paracetamol and told him he would have to work for two months to pay for it," she said. "I said to him, `Why don't you run away,' and he replied, `Run away to where? I don't have any money and I can't go home like this.'"
The campaign against slavery has taken center stage since President Lula da Silva came to power in 2002. In 2003 a national action plan drafted a blacklist of the companies involved.
Shield of impunity
Yet campaigners say a shield of impunity still exists for many slave owners and warn that until a new bill is passed allowing the confiscation of land, little progress will be made.
In the past, several politicians have been denounced for exploiting slave labour.
Last year, Senator Joao Ribeiro was fined 760,000 real after 38 men, working in slave-like conditions were found on his farm.
Rezende fled northern Para state after receiving death threats from pistoleiros (hired guns).
He claimed that the landowners reasoned the workers were uncivilized, and that they were offering them work and food.
"It is a cultural problem," Oliveira said. "The landowners say, `Everybody does this, so why should I be different?'"