Women were forced to work in slave-like conditions in a brothel in the heart of the Amazon rain forest.
A congressional panel in Brazil has summoned bosses of a company building a huge dam to be questioned within the next two weeks.
Vicente Bezerra, spokesman for the president of the panel, Congressman Arnaldo Jordy, said directors of the Belo Monte Construction Consortium have been called to "explain how a brothel could operate inside the area where the dam is being built".
He said: "There is no way the Belo Monte Construction Consortium did not know of the existence of the brothel," adding that to reach it, investigators passed through an area with signposts indicating the land belonged to the consortium.
Mr Bezerra said 18 women and one teenage girl worked in slave-like conditions in the brothel that was recently dismantled by police.
"The women were lured from to the region from all over Brazil with promises of a good jobs and high pay," he said. "But when they got there they were forced to work as prostitutes."
The teenager escaped the brothel a few weeks ago and alerted the police, he said
"We will certainly send directors to speak to the panel," said consortium press officer Fernando Santana.
"We have done nothing wrong nor do we have anything to hide."
He said the brothel was located near the Belo Monte construction site but on land that belongs to "private parties and not to the consortium". He added he did not know who owned the land.