This study examines how party size shapes voters’ likelihood of engaging in protest, moving beyond a simple winner–loser categorization of parties. In European democracies, where coalition governments are prevalent, policy-making often requires compromises among parties with differing issue positions, leading to varying levels of voter representation. Junior coalition parties, overshadowed by majority partners, have limited decision-making influence, which increases the likelihood that their voters will protest to shape policy agendas. However, smaller coalition parties still offer better representation than those in opposition. As a key indicator of a party’s capacity to represent its voters, party size significantly shapes motivations for protest among both government and opposition parties. Using data from eight waves of the European Social Survey (2004–2018), the article finds that voters of junior coalition parties are more likely to protest than those of senior coalition partners. Additionally, smaller party size correlates with a higher probability of protest participation, particularly among opposition party voters.