The company is accused of influencing the election in favor of right-wing candidate Flávio Bolsonaro, and left-wing President Lula da Silva’s staff has taken it to court.
Meta has claimed to be impartial, but a court has now given the company one day to provide evidence.
The decisive second round of the election between Lula da Silva and Flávio Bolsonaro, the son of imprisoned former right-wing president Jair Bolsonaro, will be held on Sunday.