The aim of the article is to present a new type of complaint — the so-called social media complaint or complaint 3.0. In addition to the characteristics of the genre, the article also contains the result of a study of complaints posted on Facebook by customers of two banks in Poland: ING Bank Śląski and mBank. The analyses have been carried out from the perspective of plain language, specifically the principles of relations between the sender and the receiver. The study is based on customers’ complaints and the banks’ replies posted on their fan pages. The texts (2×100 bank-customer interactions) have been analysed with regard to their content.