Public service institutions such as the judiciary, universities, and the police force derive their legitimacy from their impartial functioning. Yet, around the world, such institutions are increasingly accused of holding a left- or right-wing bias. This study examines to what extent citizens perceive ideological bias among the actors working in public service institutions, and what explains these perceptions. We collected original survey data in five European countries (Germany, the United Kingdom, Spain, Poland, and the Netherlands), measuring citizen perceptions of left-right bias among the actors working in six public service institutions. We find that bias perceptions are widespread, with some institutional actors (scientists, schoolteachers, and journalists) being associated more to the left, and others (police, judges) more to the right. Bias perceptions are more common among citizens with more political interest, lower levels of education and income, and ideologically extreme positions. Crucially, we find that the (left-right) direction of perceived bias depends on one’s own (left-right) position, such that left- and right-leaning citizens tend to associate institutional actors with the opposite (‘hostile’) ideology. Our analyses reveal cross-national and cross-institutional variation in bias perceptions and suggest that public service institutions can become politicised in the eyes of citizens. This highlights the need for further research into the contextual drivers of bias perceptions and their implications for perceived institutional legitimacy.