Some 7,000 workers at a contested dam in Brazil's Amazon region went on strike Monday demanding better working conditions, the consortium in charge of the project said.

The Belo Monte consortium said many workers joined the strike because labor unions erected barricades on the road leading to the site, located near the town of Altamira on the Xingu River in the northern Brazilian state of Para.

The workers are demanding that they get a free air fare and a nine-day break to visit their families every three months instead of the current six months. They also want a higher food allowance.

Work on the $11 billion project that has irked indigenous groups, environmentalists and local residents got under way last June.

With a capacity of 11,200 megawatts, the hydroelectric dam is portrayed by Brazil's government as a key piece of its plan to boost national energy production for one of the world's fastest-growing emerging economies.

It would be the third biggest dam in the world, after China's Three Gorges Dam and the Itaipu Dam on the border between Brazil and Paraguay.

The dam is expected to flood an area of 500 square kilometers (200 square miles) along the Xingu River and displace 16,000 people, according to the government, although some NGOs put the number at 40,000 displaced locals.

In December, a judge revoked his own order to halt work, saying the consortium had shown the dam would not impede local fishing or affect the natural flow of the river.

Indigenous groups fear that the dam will harm their way of life, while environmentalists have warned that it could lead to deforestation, methane emissions and an irreparable changes to the Xingu River's ecosystem.

The government had pledged to minimize the environmental and social impact of the dam and insisted that no traditional indigenous land was to be affected.

But its construction has been the subject of legal wrangling for decades.