Haddad made his allegations on Thursday after the newspaper Folha de Sao Paulo reported that wealthy Bolsonaro supporters had paid for messaging via third-party companies.
The paper said the agencies had spent up to 12 million reais ($3.26 million, 2.85 million euros) on “blast messaging” adverts attacking Haddad and his Workers’ Party (PT).
Haddad asked Brazil’s top court and the country’s electoral commission to investigate the allegation of illegal undisclosed funding, and said he had leads to follow, without naming names. He said that illegally-bought ads had been used ahead of the October 7 runoff campaign, from which he and Bolsonaro progressed to the head-to-head vote.
In addition, Haddad alleged that companies were poised to release a barrage of WhatsApp messages, spreading “fake news” about himself and the PT.
“There has been a criminal organization of businessmen which used illegal campaign financing to promote this candidacy and tamper with the election in the first round. And they want to do it again in the runoff,” Haddad said. “We estimate that hundreds of thousands of messages, all fake, were sent to voters to suggest they voted for my rival.”
‘No evidence of connection’
Denying the accusation in a tweet, Bolsonaro said Haddad’s Workers Party “isn’t being hurt by fake news, but by the TRUTH.”
Bolsonaro’s lawyer, Tiago Ayres, told the financial daily Valor there was no evidence of a connection between Bolsonaro’s campaign and the companies mentioned by Folha de Sao Paulo.
The row came 10 days before the run-off election that Bolsonaro — a social media-savvy, divisive figure often compared to US President Donald Trump — is predicted to win comfortably.
The 63-year-old Bolsonaro is a veteran lawmaker who was a military captain during Brazil’s military dictatorship, which ended in 1985. He has largely spurned traditional media outlets, opting to reach out to voters via his Twitter, Facebook and Instagram accounts.
Haddad, who is a former education minister and mayor, has sought to debate Bolsonaro in televised clash. Bolsonaro, recovering after a stabbing attackat a political rally last month, has so far skipped such showdowns on medical advice.
Bolsonaro’s national-conservative Social Liberal Party confirmed on Thursday that their candidate would not be taking part in debates against his rival before the runoff vote. During a video appearance on Facebook Live, Bolsonaro lifted up his shirt and displayed his colostomy bag, saying doctors had advised him that he risked medical complications if subjected to excessive strain.