Brazil is considering measures that would roll back environmental protections and make it difficult to meet its Paris climate accord targets.
The move would see the country step back from its global leadership on climate change just as the United States is also retreating.
Congress has already passed two measures that will dramatically reduce the size of protected environmental reserves.
Lawmakers are also considering substantially relaxing environmental licensing rules for infrastructure, agricultural and industrial projects.
A proposal that would change how indigenous lands are designated, potentially reducing their size and protection, is also on the table.
This comes at a time when the Amazon and Atlantic rain forests are being cut at the fastest rate in nearly a decade, and the violent struggle for control of forested land is on the rise.
"Brazil is throwing aside the opportunity to be a leader on these questions," said Marcio Astrini, co-ordinator of public policy for Greenpeace in Brazil.
"It’s very hard for someone to manage to be worse than (US President Donald) Trump on the environment, but the Brazilian government is working very hard" to do that, he added.
Brazil was long seen as a global leader on environmental issues.
As the major steward of the Amazon rain forest, its policies have a tremendous effect on global rates of carbon emissions reduction.
In conjunction with Mr Trump’s recent decision to pull the US out of the Paris agreement, Brazil’s move away from environmental regulation could jeopardise global goals.
The moves come amid political turmoil in Latin America’s largest nation.
President Michel Temer is struggling to stay in office amid corruption allegations and threats of impeachment or removal by an electoral court.
Amid the turmoil, he is trying to pass unpopular reforms he says are essential to helping Brazil’s economy shrug off a two-year recession.
Mr Temer has agreed to back a series of measures promoted by Congress’ so-called "rural caucus" - a group of lawmakers representing the interests of rural landowners, including agribusiness and ranchers - in exchange for help passing his own agenda, and hopefully avoiding impeachment.
"This government is using the environmental agenda as currency," Mr Astrini said.
In April, a week-long protest outside Congress by indigenous groups who say Mr Temer is reducing protections on their lands and allowing land-grabs by farmers and ranchers illustrated the debate.
When police fired tear gas at the protesters, they responded with spears and arrows.
Last month, Congress passed two measures that convert around 1.4 million acres of protected land, the vast majority of it in the Amazon, into areas open to logging, mining and agricultural use.
An analysis by the Institute for Amazon Environmental Research estimates the drop in protections could result in the loss of nearly 700,000 acres (280,000 hectares) of forest by 2030 and lead to the release of 140 million tons of carbon dioxide.
Nilson Leitao, a federal lawmaker from the rural caucus, disputed that the measures would lead to deforestation and noted that the area was already one of the most protected in the world.
"The people who live there... they need a life, they need to produce," he said.
Milder versions of the measures - which partially offset the losses by designating newly protected areas - began as executive orders.
But the congressional amendments have made the measures unpalatable even to Mr Temer’s own environment minister, who has recommended the president veto them, saying they would impede efforts to combat deforestation and achieve the promises Brazil made in the Paris accord.
In that agreement, Brazil vowed to cut its greenhouse gas emissions primarily through slowing and reversing deforestation, which is rising again after years of progress.
Last year, deforestation of the Amazon jumped 29% over the previous year, according to the government’s satellite monitoring, in the highest rate since 2008.
In the Atlantic rain forest, deforestation was up 58% last year.
The president has until June 19 to sign or veto the measures.