Companies led by the world's largest soy producers, the Maggi family, are pushing for a vast complex of dams to be built along the Juruena river which flows through the tribe's land. Europe buys half the soya exported from Mato Grosso.
The Enawenê Nawê, who eat no red meat, fear the fish they rely on will no longer be able to reach their spawning grounds. Some of the Indians have left their village for the first time to join the protest.
The tribe, who number only 450, are also protesting over destruction of a crucial area of their land by cattle ranchers who are cutting down the forests and polluting the rivers with pesticides.
The Enawenê Nawê have said, "The dams will bring our death, as they will raise the uncontrollable anger of the spirits."
Local ranchers say they will apply for a court injunction to remove the Enawenê Nawê blockade on highway MT-170.
"This tiny, unique tribe knows that its very survival is threatened by deforestation and the planned dams. The Brazilian government must wake up to this fact and protect the Enawenê Nawê's land before it is too late," said Survival International organization's director, Stephen Corry.