Social media platforms have for long been accused of bias by politicians of all stripes. It matters because a skewed algorithm can mean denial of outreach at crucial moments. But it has always been difficult to prove such bias, alleged mostly of US-based platforms. Now, communication among Meta employees reported last week has revealed partiality against Lula da Silva, the left-leaning incumbent up against the right-wing, Trump-friendly Flávio Bolsonaro in a close race to govern South America's biggest economy. Meta’s denial has fallen flat against the difficulties faced by millions of users in sharing campaign material. Such aberrant behaviour would worry governments and opposition politicians around the world. Before it invites stronger control of digital media, a wider discussion of implications on all sides is needed