Environmentalists consider new legislation as the destruction of a California-sized chunk of Amazon rainforest.
A congressional committee is considering legislation that would reduce the amount of forest landowners in the Amazon must leave standing as forest reserve.
"There's a real threat if this law is approved," said Jose Maria Cardoso Silva, vice president in charge of science for Conservation International in Brazil. He said the legislation would lead to the deforestation of 47 million hectares (181,500 sq. miles) in the long term.
Under a 2001 executive decree, landowners in the Amazon may only clear-cut 20 percent of their land for pasture and planting and must maintain 80 percent standing as forest reserve. Many landowners say the restrictions hinder development in the dirt-poor Amazon region, which covers nearly 60 percent of Brazilian territory.
Rep. Jorge Khoury, the committee's co-chair, denied Tuesday's hearing was the first step toward reducing the forest reserve.
"This is just one more hearing to collect information and create a report to suggest changes to the law," Khoury said in telephone interview.
But environmentalists noted there are two separate projects before congress seeking to reduce the amount of required reserve to 50 percent from the current 80 percent.
About 20 percent of Brazil's Amazon, covering some 4.1 million square kilometers (1.6 million square miles), has already been cut down.