The electoral campaign of Brazilian President Luiz Inácio Lula da Silva (known as Lula) has asked the country’s top electoral court to disqualify his right-wing challenger, Flávio Bolsonaro, accusing the social media company Meta of limiting Lula’s content to boost his opponent’s campaign. The petition was filed on Wednesday, four days before Sunday’s presidential run-off.

It asks the Electoral Court to investigate Bolsonaro and his running mate, Alfredo Gaspar, for “abuse of economic power and improper use of social network [sic]”, and to bar Bolsonaro from standing for election for eight years.

Bolsonaro, the son of former president Jair Bolsonaro, who is under house arrest, answered with a petition to disqualify Lula. He accuses the president of “abuse of political and economic power”, saying the government used personal data from official databases to send mass WhatsApp messages promoting its social programmes.

The row follows a report by United Nations experts, led by the special rapporteur on freedom of expression, who said Meta must ensure a level playing field. “Information, including from Meta employees, suggests that accounts linked to one side of the presidential race were disproportionately curtailed,” the report said. Meta, which owns WhatsApp, Instagram, and Facebook, denies favouring either side and has said it will comply with a court order to treat both candidates equally.

Bolsonaro narrowly beat Lula in the first round on 4 October, by 47% to 45%, but fell short of the 50% needed to win outright. Polls suggest Sunday’s vote will be extremely close. Lula is seeking a fourth term, while a Bolsonaro win would extend a shift to the right across Latin America that has brought conservative presidents to power in Chile, Bolivia, and Argentina.