BRASILIA (Reuters) - A Brazilian Supreme Court justice reopened a probe on Friday into suspicious cash payments involving President Jair Bolsonaro’s son Flavio, reviving an investigation that has dogged the president’s first few weeks in office.

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In a decision that revoked an earlier injunction blocking the probe, Justice Marco Aurelio Mello also ruled that the immunity from prosecution enjoyed by top elected officials should not apply to the investigation. Mello said the alleged crimes were committed before Flavio Bolsonaro took office as a federal senator.

The decision to reopen the investigation is a blow to Jair Bolsonaro, who took office last month after surging to victory in elections last year on a promise to clean up years of graft in politics.

The Supreme Court decision, which can be overturned at a later date by the full panel of justices if Bolsonaro appeals, comes on the same day Flavio Bolsonaro is sworn in as a senator, and as Brazil’s new class of federal lawmakers begin the 2019 session.

The case has shone an unflattering light on the presidential family’s long history in the rough-and-tumble world of Rio de Janeiro politics. It also threatens to weaken Jair Bolsonaro’s hand in Congress as he seeks to deliver a broad legislative plan to open up the economy, push through complex pension reform and enact a socially conservative, law-and-order agenda.

In pointed comments at the Supreme Court after Mello’s decision was announced, Vice President Hamilton Mourão said the government would not let up in the fight against corruption.

“We will not be lenient in the misconduct of public and private agents,” said Mourão, speaking on behalf of the president, who remains in hospital while he recovers from planned surgery.

The earlier Supreme Court decision to put aside the case followed a request from Flavio Bolsonaro’s lawyers for it to suspend a probe into suspicious payments to his former driver, Fabricio Queiroz.

Flavio’s lawyers argued that as a senator-elect, Bolsonaro enjoyed certain legal protections - including that any case involving him should be decided only by the top court.

The court’s subsequent injunction was widely criticized and gave ammunition to critics who noted that Bolsonaro and his politician sons have railed against the immunity from prosecution that politicians enjoy - and that Flavio invoked.

The scandal arose in December when the Council for Financial Activities Control (COAF) identified 1.2 million reais ($305,000) that flowed through the bank account of Queiroz in 2016-17. Some payments were made to the president’s wife, Michelle.

Jair Bolsonaro has said that Queiroz was repaying a personal loan to Michelle. Flavio Bolsonaro, his father and Queiroz have all said they are innocent of any crime.

However, COAF later went on to identify cash transfers worth almost 100,000 reais ($26,665) that were deposited over the course of a month into Flavio’s account, according to a television news report.

They were part of a payment for an apartment he sold, Flavio Bolsonaro said in a TV interview, but he did not clarify why the deposit had been made in such a way as to hide the origin.

Later, Flavio said he was the target of a “defamatory campaign” after news outlets reported that he employed the mother and wife of a fugitive former policeman accused of running a criminal organization.

“Should any evidence become available against my son, he will be punished like anyone else and serve his penalty,” Jair Bolsonaro told the Washington Post in an interview last month.