More than 300 Brazilian companies have been fined by the country's Ministry of Labor for using methods that can be classified as modern-day slavery, including profiting from forced work, degrading labor conditions and giving little or no compensation to employees.

The investigation into labor practices was instigated by the NGO Repórter Brasil and the Brazilian Institute to Eradicate Slave Labor (InPACTO), using freedom of information laws in order to have the information published and to "enforce society's right to transparency regarding corporate labor practices," as they explained in a press release earlier this month, according to TeleSUR.

The published blacklist reveals 340 companies in both rural and urban areas that employed people in slave-like conditions in sweatshops, farms, cattle ranches and construction, from May 2013 to May 2015. In Brazil, slave labor is defined as work performed in degrading conditions or in circumstances that potentially threaten a worker's health or life. Forced labor and debt bondage-working without pay in order to recompense off debts-are also considered to be forms of slave labor.

"The companies were fined by the labour ministry and those enslaved [have now been] released," Leonardo Sakamoto, director of Repórter Brasil, told Reuters.

The blacklist, or "dirty list," has been integral in Brazil's ongoing fight against slavery, blocking companies from directly receiving government loads and finding as well as putting restrictions on product sales, as Reuters explains. If after two years the company has paid its fines and can prove that working conditions in its facilities have been amended, it can be removed from the list.

In 2014, however, the Supreme Court of Brazil ordered the Ministry of Labor to stop publishing the blacklist — prompted by an injunction from Brazil's Real Estate Developers' Association (Abrainc), which includes the South American country's most powerful construction companies, according to Reuters. Repórter Brasil is lobbying to make the list public again, as outlined on the NGO's website.

in his discussion with Reuters, Sakamoto said that it is not yet known whether children were enslaved, nor whether the blacklisted construction companies are involved in building projects connected to the Olympics.

It is estimated that around 21 million people globally are caught in some form of forced labor, which in turn generates profits that equal more than $150 billion (USD) a year, according to the International Labour Organisation (ILO).