Brazilian President Luiz Inacio Lula da Silva and his right-wing challenger Flavio Bolsonaro are seeking each other's disqualification over allegations of electoral misconduct, escalating tensions ahead of Sunday's presidential runoff.
The rival legal challenges center on accusations of improper government messaging and social media interference as polls indicate a closely contested election.
Bolsonaro's lawyers filed a petition with Brazil's Superior Electoral Court (TSE) on Tuesday, accusing Lula of abusing his authority through the mass distribution of government communications on WhatsApp during the campaign.
The complaint alleges that government messages promoting social programmes, benefits and official initiatives reached millions of Brazilians during the election period.
It seeks to bar Lula and Social Communications Minister Sidonio Palmeira from holding public office for eight years.
Lula's campaign, meanwhile, announced plans to request Bolsonaro's disqualification on Wednesday, alleging that Meta's algorithms unfairly disadvantaged the incumbent.
Campaign coordinator Senator Camilo Santana confirmed the filing would follow a day later than initially anticipated.
Brazil's electoral court ordered Meta on Monday to demonstrate compliance with requirements for equal treatment of both campaigns within 24 hours, threatening daily fines of approximately $200,000.
Lula's campaign accused the technology company of suppressing its content while allowing Bolsonaro's material to circulate more freely.
Meta denied favoring either candidate and said Tuesday that it had implemented measures required by the court.
The company acknowledged earlier technical errors affecting some Lula advertisements and introduced restrictions allowing only registered candidates and political parties to advertise.
It also removed 720 improperly labeled AI-generated posts.
The controversy prompted demonstrations outside Meta's Sao Paulo offices on Monday, where Lula supporters protested alleged electoral interference.
Bolsonaro secured 47 percent of the first-round vote earlier this month, compared with Lula's 45 percent, leaving the candidates effectively tied in polling ahead of October 25.
The election also carries broader political implications, with Lula seeking a fourth non-consecutive term and Bolsonaro promising to free his father, former President Jair Bolsonaro, who is serving a 27-year sentence under house arrest over an attempted coup.