Green activists are bracing themselves for their "biggest fight of the decade" against a scheme that will destroy swathes of Amazon rain forest to make way for giant cattle-grazing pastures and man-made woodland.
The attack on one of the world's most fragile eco-systems comes from a powerful coalition of landowners and logging companies who want sweeping changes in Brazilian law to allow new developments on the land.
With the support of many of the country's politicians, they are pushing for a 30 per cent reduction in the rain forest in order to have larger farms, eucalyptus and pine plantations.
Greenpeace's political adviser in Brazil, Mr Flavio Monteil, said: "If this proposal becomes law, it will set the environmental movement back 30 years.
"The government is going to allow destroyers of the environment to do whatever they like without consequence."
The proposed changes to the Forest Code, which was established in 1965, would also:
reduce the protected rain forest outside the Amazon from 50 per cent to 20 per cent;
reduce the conservation area surrounding riverbanks and lagoons from 100m to 30m;
exempt smaller properties, up to 20 hectares in size, from all environmental law;
allow landowners to cut down rain forest for reasons of economic expansion, including planting crops, without applying for a licence from authorities, and
give those farmers who have built illegally on protected land amnesty from prosecution. A spokesman for the World Wildlife Fund, Mr Robert Buschbacher, said: "If this law is passed, the rain forest's fragile biodiversity will be seriously threatened.
"It will expose Brazil's forests to massive destruction and will threaten the natural habitats of endangered species."
Plans to rewrite the Forest Code were pushed through the Brazilian congress in a record six days, taking the environmental lobby by surprise.
With the influential support of the Minister for Agriculture, the Minister for Minerals and Energy and the National Council for Agriculture, the radical scheme would have instantly become law if green-minded politicians had not stepped in.
Andre Lima, an environment lawyer for the Socio-Ambient Institute, a Brazilian NGO, said: "The main problem is that there has been no public discussion of these recommendations.
"They wanted them on to the statute books without listening to any other sides of the argument. Anyone who cares about the environment should be getting ready for the biggest fight of the decade."
The Environment Minister, Sarney Filho, who also is against the proposed measures, yesterday tried to delay a final vote in congress.
Despite having a third of the world's rain forest, Brazil has already seen large-scale destruction of its native woodland. Some two-fifths of the country's rain forests have been destroyed.
Apart from providing a natural habitat for flora and fauna, the rain forest is essential for global climatic stability.