The protesters gathered outside Meta's headquarters in the Faria Lima area on Monday, accusing the company of favouring presidential candidate Flavio Bolsonaro ahead of the October 25 run-off.

Demonstrators carried placards reading 'Meta, don't meddle', 'In Brazil, Brazil decides' and 'Meta blocks pro-Lula political content'.

They demanded greater transparency from the company behind Facebook, Instagram and WhatsApp, alleging that accounts supporting Lula had been suspended and political content restricted.

"[Meta] has been interfering in the Brazilian elections . It is very serious. Since the beginning of the year, it has taken decisions to remove accounts and suspend content without giving any explanation," said Alexandre, one of the demonstrators, asserting that the situation "has intensified" as the electoral timetable advances.

Another protester claimed that account suspensions were affecting political mobilisation during the final days of campaigning.

"We are seeing many people being blocked, aren't we? Or, at times, the suspension of their accounts during this period - precisely the electoral period - just at the moment when we manage to take to the streets and the networks, aren't we? And then they are blocking a lot of people," he said.

The demonstration coincided with a ruling by Brazil's Superior Electoral Court (TSE), which ordered Meta to provide evidence within 24 hours that both campaigns receive equal treatment.

The company could face daily fines of up to one million reais, approximately $185,000, if it fails to comply.

Meta has denied favouring either presidential candidate, maintaining that its rules apply equally to all political campaigns.

The company also rejected allegations that it was interfering in Brazil's electoral process.

The dispute follows complaints from both presidential campaigns about unequal treatment on digital platforms.

Concerns increased after journalistic investigations identified differences in the responses generated by Meta's artificial intelligence tool on WhatsApp.

According to the findings, the tool generated election posters when prompted with "Flavio 22" but rejected similar requests containing "Lula 13".

Meta attributed the difference to a problem with its filters, explaining that the system did not always recognise "Flavio" as a reference to the presidential candidate.

The company said the issue had been corrected.

The controversy comes during the final days of Brazil's presidential campaign, with Lula and Bolsonaro preparing to face each other in the October 25 run-off following a closely contested first round.