The Covid-19 pandemic has struck the Canadian economy hard and Quebec unions have had to quickly make significant adaptations. Based on field research funded by the Social Sciences and Humanities Research Council (SSHRC) of Canada, in partnership with one of Quebec's main union confederations, our article analyzes the state of union representation in eight economic sectors, with the arrival of the closures linked to the Covid-19 pandemic. The practices before, during and after the pandemic are compared. The argument of our article will be threefold: firstly, on a practical level, our results provide strong evidence indicating that joining a union in times of crisis protects workers from immediate harmful consequences, by reducing the scale of mass layoffs, by facilitating access to protective equipment and by negotiating material compensation for essential jobs. Secondly, the article contributes to the literature on the advantage of unions and on union renewal, as well as to an actor-centric view of labor relations, positioning unions as "strategic actors" (Hyman 2007). Finally, the article supports the idea that unions are agents of "institutional experimentation" (Ferreras et collab., 2020) when there are profound ruptures, creatively using the institutional levers at their disposal and thus shaping the world of post Covid work.