In this study, the impact of platform-mediated visibility on Portuguese citizens' responses to the 2024 vehicle circulation tax (IUC) is investigated and the fiscal attitudes that drove these reactions are identified. A thematic and multiple correspondence analysis was performed on 622 comments from an e-participation platform, and the results were interpreted through the frameworks of participatory democracy, platformization and tax compliance. Reactions cluster into five main themes: “fairness-taxation,” “trust in government,” “corruption-income,” “tax awareness” and “not mentioned.” Affective, anti-elite frames were given disproportionate visibility and knowledge-oriented contributions, such as “tax awareness,” remained comparatively peripheral. The following three lines of debate were identified: (1) tax literacy and fiscal justice, (2) perceived corruption and inequality of income and (3) trust in government, usually expressed in the form of disillusionment. The petition served, on one hand, as a tool of mobilization, and, on the other, as a place for political contestation, increasing the risk of polarization. This is a single-country study based on public comments. To be generalized, the findings should be compared with different policies and platforms in other contexts through longitudinal or mixed-methods designs that link online discourse to policy responsiveness. This study underscores the importance of aligning policy design with transparent and responsive communication. Policymakers should address taxpayer concerns to strengthen legitimacy and tax compliance while mitigating polarization. It offers a novel empirical insight into digital fiscal participation. The study demonstrates that algorithmic visibility and affective salience increase anti-elite expressions but decrease informational depth, which in turn lowers perceived tax legitimacy by changing perceptions of fairness, trust and corruption. The study developed an analytical framework that can be replicated and bridges the gap between tax compliance, media logic and platform studies.

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Citizen participation,Public opinion,Tax policy