The Brazilian government will start deploying a small army of drones as part of its latest effort to eradicate human trafficking in remote parts of the country.

Starting next month in the state of Rio de Janeiro, six drones mounted with video cameras will be sent to fly around and record businesses in rural areas suspected of forcing workers to toil away in slave-like conditions. Exactly what will be done with the footage is still unclear.

"Drones don't substitute the inspector's physical presence, but they will be useful out in the country, in the case of farms that are hard to reach by road, for example," Bruno Barcia Lopes, coordinator of Rural Supervision for Rio de Janeiro's Labor Secretariat, told the Thomson Reuters Foundation.

The labor ministry in Brazil defines slave labor as work done in degrading conditions for less than minimum wage. For years, activists and NGOs have decried slave labor in Brazil's rural sector, including the charcoal production and cattle-farming industries.

There are no reliable statistics about slave labor in Brazil, so it's difficult to know the extent of the problem, but estimates range between 25,000 and 40,000 people. An estimated 1.8 million people work for little or no pay across Latin America.

But the government has stepped up in recent years to address the problem and the country's labor ministry, in particular, has made it a main priority. In the mid-1990s, the labor minister launched its Special Mobile Enforcement Group that teamed up with law enforcement and prosecutors to hunt down and raid farms and other companies suspected of abusing workers.

And according to the Guardian, more than 400 Brazilian companies comprising 30 percent of Brazil's GDP signed a national pact to eradicate slavery in 2005.

The drone plan couldn't come at a better time, since one of Brazil's most effective and influential tools against slavery in the country was recently compromised.

In 2003, the government got even more aggressive and began publishing a list of companies found to be using slave labor, known as the "dirty list." Companies that made it on the list, which numbered as many as 600, were subjected to sanctions often boycotted around the world and also barred from getting government and private loans. The company could get off the list if, after two years, they proved they had changed their ways.

Last year, the company that built the World Cup stadium in Brazil was added to the dirty list after government officials accused it of subjecting more than 100 workers to squalid conditions and long hours. The list was upheld by the International Labor Organization and other human rights groups as an inspiring approach.

However, the Supreme Court in Brazil ruled to suspend the restrictions imposed by the list last December after a group of real estate companies filed an injunction against it, claiming its restrictions were too much.

Anti-human trafficking groups were furious at the ruling, which they say creates "a normative vacuum that allows nearly 600 companies and persons exploiting slave labor to benefit from publish funding and tax advantages."

According to Brazil's ministry of labor, 41,451 workers across Brazil were "rescued" from slave-like conditions from 1995 to 2011, most of whom were working under debt bondage. The Special Mobile Groups Inspection reportedly rescued more than 2,000 workers in 2013. It's unclear if any those workers are better off now.

"We can't say things are better, or that slave labor has migrated to the cities, and it's almost impossible to calculate numbers," Leonardo Sakamoto, head of anti-slavery group Repórter Brail told Reuters. "Slave labor is like Silly Putty. Every time you squeeze it, it assumes a different form."

In what's believed to be the first proposal of its kind, Kevin Bales, a well-known American abolitionist and co-founder of NGO Free the Slave, said in 2013 he would use drones with cameras to film slave labor in the fishing camps in India and a tiger sanctuary in Bangladesh.

His plan was to partner with a British filmmaker and turn the footage into a documentary and, ultimately, use the information to help free those trapped in forced labor.

But it wasn't well-received by local activists who called it a well-intentioned publicity stunt that didn't address the underlying causes of exploitative labor.

According to the International Labor Organization, there are around 21 million people worldwide trapped in some form of forced labor. The United Nations estimates that trafficking in human is the third largest criminal industry, behind drugs and guns.

Brazil was the last country in the Americas to officially abolish slave labor in 1888.