Bolsonaro won the 2018 presidential vote, but claims without evidence his margin of victory would have been larger if not for widespread fraud in Brazil's electronic voting system.
The far-right president has brought the allegation back to the fore as he prepares to launch his reelection campaign ahead of the October 2022 vote — raising fears he could refuse to accept the result if defeated.
Stepping into the fray, YouTube's Brazil office said it would remove videos that "promote false allegations that widespread fraud, errors or technical problems changed the result" of the 2018 election.
Political analysts warn that Bolsonaro could be preparing to follow in the footsteps of his political role model, former US president Donald Trump, who refused to accept his 2020 election defeat, alleging widespread vote-rigging.
Bolsonaro currently trails in the polls to his likely opponent, leftist ex-president Luiz Inacio Lula da Silva.
Brazil is deeply polarised heading into the elections, which look set to be fertile ground for disinformation wars on social media, much like the 2018 campaign.
YouTube's move comes after a Supreme Court judge last week ruled to block online messaging platform Telegram for refusing to comply with requests from Brazilian authorities, including to remove disinformation.
The ban was lifted after Telegram agreed to remove the material, including an August post by Bolsonaro in which he questioned, without evidence, the reliability of Brazil's electronic voting system, in use since 1996.
Bolsonaro has also had posts removed from YouTube, Facebook, and Instagram for spreading disinformation.
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