Brazil's president, Dilma Rousseff, arrives for a news conference at the Planalto Palace, in Brasilia, Brazil on Dec. 2. (Ueslei Marcelino/Reuters)

A senior politician on Wednesday gave the go-ahead for impeachment proceedings against President Dilma Rousseff, adding to the turmoil in South America’s economic giant.

Although a final impeachment vote by Brazil’s Congress is unlikely before 2016, the move represents the biggest threat yet to the beleaguered president, who has grappled with a stalled economy, demonstrations and historically low approval ratings since being narrowly reelected a year ago.

“It is a watershed,” said David Fleischer, a political science professor at the University of Brasília.

Eduardo Cunha, speaker of Brazil’s Chamber of Deputies, approved the launching of the impeachment proceedings. The process will examine Rousseff’s possible connection to a huge corruption scandal at the state-controlled oil company Petrobras and the decision by Petrobras to buy an overpriced oil refinery in Pasadena, Tex., in 2006 when Rousseff was the company’s board chairwoman, officials said. More seriously, the proceedings will focus on allegations that she broke the law through irregularities in the government’s accounting and spending.

In a statement, Rousseff said she was indignant and denied she had done anything wrong. “My past and my present attest to my integrity and my unquestionable commitment to the laws and public affairs,” she said.

Cunha has been at odds with the president since he was voted speaker in February, even though his political group, the Party of the Brazilian Democratic Movement, is the principal ally of Rousseff’s Workers’ Party in the governing coalition.

Cunha is one of dozens of lawmakers being investigated in connection with the Petrobras scandal and faces an impeachment process by a chamber ethics committee. Analysts saw his decision Wednesday as part of a tough game of political poker. They note it came after three key Workers’ Party deputies on the ethics committee voted for the investigation into his activities to continue.

“He’s a player and he knows how to play,” said Fleischer

The government is likely to legally challenge the impeachment, said Sylvio Costa, founder of the political news site Congress In Focus.

Under Brazil’s impeachment procedures, a committee is formed to consider the allegations, which are then voted on by the Chamber of Deputies. If two-thirds of the chamber, or 342 deputies, vote in favor of impeachment, Rousseff is temporarily suspended awaiting a final vote by the Senate. There, a two-thirds vote is needed to remove her from office.

Constitutional expert Ives Gandra Martins, who wrote in a legal opinion this year that there was a juridical basis for impeachment, said the process would ultimately be decided politically.

“If the deputies believe the country has become ungovernable and the population is going into the streets, impeachment will stick,” he said.

The impeachment decision comes as Rousseff has faced rising unemployment and a withering economy. News on Tuesday that the economy had shrunk 1.7 percent in the third quarter of this year added to her woes.

The Petrobras scandal involves kickbacks to politicians, middlemen and executives. The financial accusations reflect a court decision that the Rousseff administration’s accounting practices in 2014 violated the law.

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