Brazil’s Congress has voted in favor of an amendment strengthening the penalties for employers who hold workers in slave-like conditions, a key step to combating modern-day slavery, despite the significant challenges that remain.

Last month, Brazil’s lower legislative house approved a constitutional amendment allowing for the expropriation of land used by businesses that employ workers in slave-like conditions. A press release by humanitarian agency Catholic Relief Services called it “the strongest legal instrument ever passed in Brazil for combating slave labor.” In addition to potentially having their property seized without compensation, those found guilty of exploiting slave labor will face pre-existing penalties, including fines and up to eight years in prison.

Brazil’s Senate still needs to determine the official criteria for defining slave-like conditions and the process by which land is seized, but as the Associated Press reported, this will likely be a speedy process. The main hurdle facing the amendment was probably its approval by the lower house, the Chamber of Deputies.

The amendment, known as PEC 438, was first introduced in 1995. But it only passed a first round of voting in Brazil’s Congress in 2004, after three labor auditors and their driver were killed earlier that year in Unaí, Minas Gerais state. The auditors had reportedly issued fines on multiple farms in that state for poor treatment of their labor force. Even though the UN’s special rapporteur urged Brazil’s Congress to adopt a version of the law in 2010, it continued to drag in Congress until very recently.

The amendment is a major victory in Brazil’s fight against slave labor, a practice found in a wide range of industries. Workers are often recruited by fixers called “gatos” for jobs that have much worse conditions than advertised, and then intimidated into staying.

Expropriating property might yet prove to be the most effective way of penalizing the businesses guilty of exploiting slave labor. Many of these businesses are based in Brazil’s more rural and isolated regions, and involve work like mining and agriculture. Without land, they cannot continue to be profitable. Other strategies deployed by the government — such as fining the companies, or focusing on identifying and freeing the captive workers — have so far proven to have little teeth.

Brazil has reportedly fined companies some $35 million since 1994, when the government began a focused crackdown on slave labor. But Brazil’s slow-moving judicial system has allowed many offenders to avoid fines and jail time. Fines alone won’t work because many businesses aren’t concerned with fines, but with their ability to receive loans from banks, a Labor Ministry spokesperson told the AP earlier this year.

And even though labor authorities are rescuing more people from slavery than ever before, such an approach has arguably only proved to be a short-term solution. In 2011, exploited workers were rescued in 19 out of a total of Brazil’s 26 states, evidence of the government’s expanded enforcement efforts. The Labor Ministry has said that some 42,000 slaves have been freed since 1993; 2010 alone reportedly saw 2,628 workers rescued. But these rescue efforts haven’t made much of a dent in the total number of slaves in the country. In March 2012, Rogenir Costa, head of Brazil programs for Catholic Relief Services, told InSight Crime there are still between an estimated 25,000 and 40,000 slaves in Brazil.

By allowing authorities to expropriate land, the new amendment could prove to be a more effective deterrent for employers that are flagrantly violating labor laws. Another potent weapon is the government’s “dirty list” (see list hosted on the website of Reporter Brasil, a Brazilian anti-slavery NGO) of companies that employ laborers in slave-like conditions. The list, established in 2005, namechecks 300 companies, and essentially makes it impossible for them to receive credit from any government or private bank in Brazil until they pay fines and labor-related taxes. By attacking both the credit and the property of companies that keep slaves, the government is arguably hitting such employers where it really hurts.

Nevertheless, the amendment doesn’t provide a set definition for slave labor; nor does it lay out the details for how land should be seized. Brazil’s powerful agricultural lobby may push to keep the rules complex so they can take advantage of loopholes or bureaucratic gridlock, as they have in the past. Catholic Relief Services representative Rogenir Costa told InSight Crime that this remains the principal challenge to the amendment’s potential effectiveness.

There are other reasons why enforcing a new anti-slavery law will be difficult: slave labor had been linked to some of Brazil’s most profitable and globalized industries. One investigation by environmental NGO Greenpeace (download pdf) found that a Brazilian steel mill, which exports iron to a US company, sources its material from local businesses involved in slavery and illicit mining. These businesses reportedly rely on fraud to cover their labor and environmental violations, as they frequently operate with false licenses or may establish front companies to cover their tracks. Such companies act as the main supplier to a Brazilian steel mill which exports pig iron, a raw material, to a US factory, where iron is processed for automakers Ford, General Motors, BMW, Mercedes, and Nissan.

Additionally, by allowing for the expropriation of property, the new amendment raises the stakes for employers reliant on slave labor. It is possible that these stricter penalties could incentivize companies to use extreme measures to ensure they don’t get caught. Some rural agri-businesses are reportedly linked to armed gangs, some of which are made up of serving, off-duty, or retired policemen. One reflection of this danger is that labor activists of all types are frequently threatened in Brazil. One prominent activist who campaigned against illegal logging, an industry with close ties to slavery, was recently forced to flee her home. Homicide cases in rural areas are rarely brought to justice: just 80 hitmen and 15 landowners have been convicted of the crime in the past two decades, although more than a thousand of land activists have been murdered.

Authorities have taken other moves towards increasing penalties against employers who keep slaves. Notably, a panel of jurists updating the country’s penal code have added the employment of workers in slave-like conditions to a list of so-called heinous crimes. This doubles the possible detention date for those charged with labor violations from 30 to 60 days.

It’s clear that anti-slavery activists now have an expanded arsenal of legal tools for ensuring that employers stay in line. But Brazil still has a powerful lobby whose interests lie in exploiting slave labor, and there are undeniable challenges ahead.