Jair Bolsonaro has long claimed that the country's electoral system is vulnerable to cheating and ahead of the October 2022 election, when he is expected to seek re - election, his attacks have intensified.
In opinion polls, Bolsonaro lags far behind former left-wing President Luiz Inácio da Silva in the race for the presidency, and critics say Bolsonaro, like US President Donald Trump, with his talk of electoral fraud is trying to cast doubt on the people.
It would make it easier for him not to accept a possible defeat.
Two investigations
Earlier this week, the country's electoral authority TSE announced that it had launched an investigation into the president's allegations, and the TSE also asked the country's Supreme Court to investigate whether Bolsonaro's attacks on the electoral system on social media are criminal and threaten democracy in Brazil.
In his ruling, the HD judge follows the election authority's line and states that Bolsonaro must be investigated for his allegations.
In its own investigation, the electoral authority will, among other things, investigate whether the president has abused his office and whether he has used official communication channels in an inappropriate manner.
"I will continue to exercise my right to speak out, to criticize, to listen to and, above all, to respond to the will of the people," the president said on Tuesday when the TSE investigation became known.
Bolsonaro has called for a departure from the completely electronic voting system and for paper copies to be created for each vote cast.
This is so that you can count votes in the event of any suspicion of cheating, he says.
He also says he may not recognize next year's election results unless the system is changed.
According to TSE, since the introduction of the electronic voting system in 1996, there has been no documented case of electoral fraud.
On Thursday, a congressional committee will vote on Bolsonaro's proposal for printed ballot papers.