An ongoing investigation into graft at Brazil's state-run oil giant Petrobras threatens to cause more headaches for newly-installed interim President Michel Temer, after forcing the removal of a minister in his cabinet earlier this week.

Romero Juca, Temer's planning minister, was forced out of office this week after leaked tapes appeared to show him in favor of impeaching President Dilma Rousseff as a way to stop the Petrobras investigation from going further.

Rousseff, a member of the Workers' Party (PT), is suspended pending an impeachment trial, and Temer, who had been her vice president, took office less than two weeks ago and brought in a whole new cabinet.

Juca says his conversation was misinterpreted, but stepped down in light of the damning revelation. Juca is still vice president of Temer's ruling center-right Brazilian Democratic Movement Party (PMDB).

Three other current cabinet ministers from the same party are also under investigation for their role in the massive bribery and embezzlement scheme centering around Petrobras.

The probe, known as Operation Car Wash, has already brought dozens of high-ranking officials and business leaders to disgrace.

Started under Rousseff's watch, the investigation, in a surprise twist, made it easier for her political rivals to mount an impeachment campaign against her, and it now threatens to destabilize the interim government as well.

On May 24, in another taped conversation, Senate speaker Renan Calheiros, also of the PMDB, said politicians "are afraid" of Operation Car Wash, especially former presidential candidate Aecio Neves, who is the president of the Brazilian Social Democracy Party (PSDB) and Temer's main ally.

Rousseff defeated Neves in the 2014 presidential elections and won a second term.

And other leaked tapes show the PMDB attempted to influence Judge Teori Zavascki, the Supreme Court's rapporteur on Operation Car Wash.

In a tape aired by Brazilian news network Globo TV, Calheiros and former President Jose Sarney (1985-1990) are heard discussing ways to pressure Zavascki using their contacts in the judicial sector.

On Thursday, Antonio Bochenek, president of the Association of Federal Judges, said the members of the judicial system will not be swayed by political operatives.

"There has always been pressure on the judicial branch, but what is important is for justice to perform its functions and for the magistrates not to give in to any type of pressure," he said.

According to the regional daily Folha de Sao Paulo, which leaked the tapes that condemned Juca, the Public Prosecutor's Office (Public Ministry) is in possession of more tapes and could cause anxiety among the political class.

The leaks and scandals are weakening the government's hand in negotiating reforms with lawmakers, according to financial consulting firm Eurasia.

The PMDB's capacity to negotiate with the Chamber of Deputies was hampered after its leading legislator, Lower House speaker Eduardo Cunha, was suspended from his position following a Supreme Court decision.