The authorities in Brazil say they have dismantled a criminal organisation they believe was the “biggest destroyer” of the Amazon rainforest.
The gang is accused of invading, logging and burning large areas of public land and selling these illegally for farming and grazing.
In a statement, Brazilian Federal Police said the group committed crimes worth more than $220m (£134m).
A federal judge has issued 14 arrest warrants for alleged gang members.
Twenty-two search warrants were also issued and four suspects are being called in for questioning.
The police operation covers four Brazilian states, including Sao Paulo.
Five men and a woman have already been arrested in Para state in the north of the country, Globo news reported.
The BBC’s Wyre Davies in Rio de Janeiro says details are still sketchy, partly because the police operation is focused on one of the most remote and inaccessible parts of the Amazon region.
Political and police corruption is still rife in Brazil’s interior, our correspondent adds.
That problem coupled with alleged ineptitude on the part of the federal government means that loggers and illegal miners are able to operate with impunity, he says.
The police announced the operation in a statement: “The Federal Police carried out today Operation Chestnut Tree designed to dismantle a criminal organisation specialising in land grabbing and environmental crimes in the city of Novo Progresso, in the south-western region of Para.
“Those involved in these criminal actions are considered the greatest destroyers of the Brazilian Amazon rainforest.”
The group members face charges of invading public land, theft, environmental crimes, forgery, conspiracy, tax evasion and money laundering.
They could be sentenced to up to 50 years in jail, although the maximum length that can be served by law in a Brazilian prison is 30 years.
Last year, the Brazilian government said the rate of deforestation in the Amazon increased by 28% between August 2012 and July 2013, after years of decline.
It made a commitment in 2009 to reduce Amazon deforestation by 80% by the year 2020.
Brazil is home to the biggest area of Amazon rainforest, a vast region where one in 10 known species on Earth and half of the planet’s remaining tropical forests are found, according to the leading conservation organisation WWF.