Brazil's Supreme Federal Court has ordered an inquiry into the sale of protected areas of the Amazon rainforest via Facebook.
It follows a BBC investigation, which revealed plots as large as 1,000 football pitches listed among the platform's Marketplace classified ads.
The court is asking the government to "take the appropriate civil and criminal measures".
Facebook has said it is "ready to work with local authorities".
But the tech firm has indicated it will not take independent action of its own to halt the trade.
The Amazon is the largest rainforest in the world and a vital carbon store that slows down the pace of global warming. It is home to about three million species of plants and animals, and one million indigenous people.
Brazilian Supreme Court Justice Luís Roberto Barroso has asked the country's attorney general and Ministry of Justice to investigate the BBC's findings.
He was already overseeing a lawsuit brought to the Supreme Federal Court by an NGO - the Articulation of Indigenous Peoples of Brazil - and six political parties.
The plaintiffs have accused the government of failing to do enough to prevent the coronavirus from affecting indigenous communities.
The judge took the decision to extend the case to include the Facebook ads.
And he drew particular attention to the Uru Eu Wau Wau community. The BBC's documentary reported that land inside a reserve used by the indigenous group had been listed for sale for the equivalent of about £16,400 in local currency.
The BBC has flagged up some of the ads involved to Facebook, but the social media giant has failed to remove them.
The listings include areas inside indigenous territories and national forests, which have protected status.
Some feature satellite images and GPS co-ordinates. Many of the sellers admit to not being able to prove legal ownership.
To find them, users need only type the Portuguese for terms such as "forest", "native jungle" and "timber" into Facebook Marketplace's search tool, and pick an Amazonian municipality as the desired location.
The BBC arranged meetings between four sellers on Facebook and an undercover operative posing as a lawyer, who claimed to represent wealthy investors.
The sellers caught on hidden camera were illegally selling and clearing rainforest so it could be used as cattle pasture and farmland.
The head of the Brazilian Senate's Environment Commission, Senator Jaques Wagner, has described the land deals as "criminal".
He said his panel of lawmakers would write to Facebook demanding it "review its policy so that this practice is curbed".
Facebook has previously indicated it believes the task of trying to deduce which sales are illegal is too complex for it to carry out itself.
But one congressman mocked this explanation.
"What is the difference between selling stolen land with violence against indigenous rights on Facebook and selling narcotics through the platform?" asked Nilto Tatto, a member of the lower house's environment commission.
"Can Facebook then be used to sell narcotics? As a parliamentarian, I will ask this question."
Brazil's government has faced international criticism for failing to curb deforestation, which is at a 12-year high.
Conservationists have accused the country's President Jair Bolsonaro of encouraging loggers and farmers to clear parts of the rainforest.
And some of the sellers captured on hidden camera by the BBC said they viewed him as an ally.
The BBC approached Brazil's Minister of the Environment Ricardo Salles with the findings of its investigation.
He said: "President Jair Bolsonaro's government has always made it clear that his is a zero-tolerance government for any crime, including environmental ones."
A UN Environment Programme spokesperson told the BBC: "Illegal deforestation undermines international treaties and commitments, including the Paris Agreement and the Convention on Biological Diversity."
Watch Our World: Selling the Amazon on BBC iPlayer here.