The Brazilian Supreme Federal Court has ordered an investigation into the sale of protected areas of the Amazon rainforest via Facebook.
What follows is a BBC investigation that revealed plots as large as 1,000 football fields listed among the ads on the Marketplace platform.
The court is asking the government to “take appropriate civil and punitive measures”.
Facebook said it was “ready to cooperate with local authorities”.
But the technology company has announced it will not take action on its own to stop the trade.
The Amazon is the largest rainforest in the world and a vital carbon stock that is slowing the pace of global warming. It is home to about three million species of plants and animals and a million indigenous people.
Brazilian Supreme Court Judge Luís Roberto Barroso has asked the Attorney General and the Ministry of Justice to investigate the BBC’s findings.
He has already overseen a lawsuit filed in the Supreme Federal Court by an NGO – the Articulation of the Indigenous Peoples of Brazil – and six political parties.
Prosecutors accused the government of not doing enough to prevent the coronavirus from affecting indigenous communities.
The judge ruled to extend the case to Facebook ads.
And he drew particular attention to the Uru Eu Wau Wau community. A BBC documentary reported that land within the reserve used by the indigenous group was put up for sale for the equivalent of around £ 16,400 in local currency.
The BBC reported some of the ads included on Facebook, but the social media giant failed to remove them.
The lists include areas within indigenous territories and national forests, which have protected status.
Some contain satellite images and GPS coordinates. Many sellers admit that they cannot prove legal ownership.
To find them, users only need to type Portuguese for terms such as “forest”, “native jungle” and “tree” into the Facebook Marketplace search tool and select the desired location as an Amazon municipality.
The BBC has arranged meetings between four sellers on Facebook and an undercover operative posing as a lawyer, who claimed to represent wealthy investors.
Vendors caught with a hidden camera illegally sold and cleaned the rainforest so that it could be used as livestock pasture and arable land.
The head of the Brazilian Senate’s environmental commission, Senator Jaques Wagner, described the land deal as “criminal”.
He said his commission of deputies would write to Facebook asking it to “review its policy to combat the practice”.
Facebook has previously hinted that it believes the task of trying to determine which sale is illegal is too complex to be done on its own.
But one congressman scoffed at this explanation.
“What is the difference between selling stolen land by violence against indigenous rights on Facebook and selling narcotics through the platform?” asked Nilto Tatto, a member of the lower house’s environmental commission.
“Can Facebook then be used to sell narcotics? I will ask this question as a parliamentarian.”
The Brazilian government has faced international criticism for failing to combat deforestation, which is at its peak of 12 years.
Nature conservationists have accused President Jair Bolsonar of encouraging loggers and farmers to clear parts of the rainforest.
And some of the vendors cultivated by the BBC on a hidden camera said they considered him an ally.
The BBC has found Brazilian Environment Minister Ricardo Salles with the findings of his investigation.
He said: “The government of President Jair Bolsonar has always made it clear that the government has zero tolerance for any crime, including those involving the environment.”
A spokesman for the UN Environment Program told the BBC: “Illegal deforestation undermines international treaties and obligations, including the Paris Agreement and the Convention on Biological Diversity.”
To watch Our world: Amazon sales on BBC iPlayer here.