In recent weeks, a new character has entered Brazilian politics – Pixuleco, a giant inflatable doll made in the likeness of former president Luiz Inácio Lula da Silva and dressed in a prison outfit.

Wielded by activists in protests against president Dilma Rousseff, Mr Lula da Silva’s protégé from his ruling Workers’ Party, or PT, the word “pixuleco” is a slang term for bribes that police say were used by those involved in a giant corruption scandal at state-owned oil group Petrobras, much of it during Lula’s presidency.

This week opponents of Ms Rousseff, incensed by allegations that “pixulecos” mostly involving ruling coalition politicians have cost Petrobras at least R$6bn (US$1.5bn), took their campaign to congress by filing a petition for impeachment with the speaker of the lower house Eduardo Cunha.

While such petitions are not uncommon in Brazil – any citizen has the right to lodge one – what was significant this time was the author: Hélio Bicudo, one of the founders of the PT, who left the party in disgust over an earlier scandal involving Mr Lula da Silva in 2005.

“I’m a doctor in impeachment,” the 93-year-old told journalists this week. He was referring to his key role in Brazil’s only successful impeachment movement, the removal by congress of former president Fernando Collor in 1992 for alleged corruption.

The petition from Mr Bicudo, which was backed by the opposition in congress, marks the start of what could be a long process to try to topple the former Marxist guerrilla only nine months into her second four-year term.

While analysts still rate the chances of Ms Rousseff falling from office as less than 50 per cent, the calls for impeachment promise to be another destabilising factor for a president who is struggling with record low popularity, a rebellious congress and a deepening recession.

“The odds of impeachment happening from now to 2016 will remain relatively high,” said João Augusto de Castro Neves of Eurasia Group. The consultancy recently raised the probability of impeachment to 40 per cent from 30 per cent.

But he said after 2016 the window for impeachment will close with the approach of the next election in 2018.

In his petition, Mr Bicudo and an associate, Miguel Reale Júnior, a former minister of justice with ex-president Fernando Henrique Cardoso from the centrist PSDB, now the main opposition party, cited the Rousseff government’s handling of the 2014 federal budget for their action.

The government accounts watchdog, the TCU, is investigating allegations the accounts were fiddled to produce a more politically acceptable budget deficit. A finding against the president, who denies the charges, could be used by congress as a basis for impeachment.

“Just as we fought against the dictatorship of arms, now we are fighting against the dictatorship of bribes,” said Mr Reale, on delivering the petition to congress. He was referring to Brazil’s military dictatorship between 1964 and 1984.

Constitutional experts say, however, that the impeachment process is complicated. The petition first needs to be accepted by a majority of congress.

The protagonists will need to then prove the president committed a crime that is relevant to her current mandate in office. While impeachments are highly political, essentially a trial of the president by the senate, they are closely supervised by the Supreme Court to ensure they stick to the law.

“What’s happening in Brazil at the moment is an economic crisis but there is no act that links the president to something illegal,” said Joaquim Falcão of FGV Direito Rio, an academic institution.

Despite the difficulties, the debate over impeachment is heating up as Brazil’s elite contemplate an economy heading into freefall this year and next with Ms Rousseff’s government flip-flopping over how to arrest a growing budget deficit.

This week, she accused those of seeking to benefit from the crisis to seize power as “golpistas”, or coup plotters. Mr Bicudo responded: “Impeachment is not coup-plotting, it is a remedy prescribed by the constitution.”