An indigenous leader delivered a petition opposing the project signed by more than half a million people.
Environmentalists say the dam in the Amazon river basin will harm the world's biggest tropical rainforest.
Another tribal leader said he and his tribe had not been given enough information about the project.
Ireo Kayapo said that if his tribe were to be driven from its land, "there'll be war and blood will be spilled."
For more on Amazon Indians in fiction, see No Indians in Off the Map and Twilight's Amazon Coven. For more on Amazon Indians in reality, see Cameron's and Weaver's Anti-Dam Films and Amazon Indian Students on the Net.
Below: "Kaiapo Indians make their voices heard outside the National Congress in Brasilia." I presume the Kaiapo have dressed this way to make a point. Note that the lead Indian is wearing glasses.