Numerous democratic innovations have tried to promote the ideal of social and political inclusion. This value was at the core of associative democracy and citizen advisory councils, which rely on associations and individual citizens to represent diverse voices. However, recent research has found that these spaces are not particularly inclusive: inequalities in associationism and biased mobilisation play a central role. In this respect, the article argues that previous studies have not fully explained how institutional design and institutional dynamics can be penetrated by class inequalities. The type of participation labour significantly influences who participates and why, becoming a central exclusionary factor. With this idea in mind, we analyse two surveys and ninety-six interviews with Spanish council participants, which reveal that these spaces are highly professionalised. Their design and the planned tasks shape associations’ mobilisation strategies, leading to the prioritisation of professionals. Also, the participation labour requires specific skills linked to cultural capital, technical knowledge and dispassionate discourse, making involvement exigent and exclusive regarding education and social class. In the end, institutional design and participation labour can discourage popular participation, even if it was not intended.