In this online citizens’ assembly experiment, we study how citizens decide to act against climate change. We ask our participants, randomly assigned to small groups, to vote by plurality for a fictional carbon tax. Our goal is to test how citizens suggest and select policy alternatives in small assemblies. Does deliberation help to process information, focus attention, or persuade individuals to change their minds? Whether deliberation in citizens assemblies is effective seems to depend on context and set-up, but these aspects have rarely been randomised before. We suggest that contextual factors can induce strategic behaviour and therefore confound deliberative effects. Building on the citizens-candidate model we investigate strategic entry in favour of different tax levels, and test how deliberation affects entry, vote choices, and voting outcomes. We present the results from our pre-registered experimental design.