James Cameron and Sigourney Weaver are among high-profile opponents of the dam
A Brazilian court has overturned a ruling that could have delayed building a massive dam on an Amazon tributary.
A judge ruled bidding can go ahead next week for contracts to build the Belo Monte dam on the River Xingu. It would be the third largest dam in the world.
The dam is opposed by indigenous groups and environmentalists.
They say thousands of indigenous people will be displaced and a sensitive ecosystem damaged. The government says it is crucial for economic development.
In a statement, campaign group Amazon Watch said "the battle is not over".
Indigenous tribes say the Belo Monte dam poses a threat to their way of life
"We are committed to supporting Brazilian indigenous peoples who have vowed to fight to stop the Belo Monte dam.
"This dam is one of the most destructive projects ever undertaken in the Amazon."
The proposal to build a hydro-electric dam on the Xingu river, a tributary of the Amazon in the northern state of Para, has long been a source of controversy.
The initial project was abandoned in the 1990s amid widespread protests both in Brazil and around the world. Canadian film director James Cameron and US actress Sigourney Weaver are among the high-profile opponents of the project.
Environmental groups say the Belo Monte dam will cause devastation in a large area of the rainforest and threaten the survival of indigenous groups.
They say the lives of up to 40,000 people could be affected as 500 sq km of land would be flooded.
However, the government says whoever is awarded the project will have to pay $800m to protect the environment.
The government also says the scheme has been modified to take account of fears that it would threaten the way of life of the indigenous peoples who live in the area.
When it is completed, Belo Monte would be third largest hydro-electric dam in the world, after the Three Gorges in China and Itaipu, which is jointly run by Brazil and Paraguay. It is expected to provide electricity to 23 million Brazilian homes.
With Brazil's economy continuing to show signs of growth, ministers say hydro-electric plants are a vital way to ensure power supplies over the next decade - and at least 70 dams are said to be planned for the Amazon region.
Critics say the Belo Monte plant will be hugely inefficient, generating less than 10% of its capacity during the three to four months of the low-water season.