It's published online first on 27th April 2010. In advanced democracies, unions influence industrial relations through collective action and law. They also maintain influence in politics through their alliances with labour parties. But the weakness of some labour movements, most apparent in falling membership, raises questions about their capacity to shape future industrial relations policy, reach voters and maintain their party alliances. Drawing on literature in industrial relations and political sociology, this article provides a framework for understanding how the Australian union movement successfully campaigned against the conservative Howard government's labour laws called WorkChoices. We characterize the union movement's campaign — Your Rights at Work — as a form of political organizing that responded to both shifting state strategy and the limits of traditional defences constituted by industrial action, legal protection and reliance on the Labor Party. Political mobilizations produce different kinds of impacts. Given that the campaign relied on a sophisticated electoral strategy, we analyse Australian Election Study (AES) 2007 data to assess its impact on voters and on activism. We find that the campaign increased the salience of industrial relations to voters, that union activism jumped in the lead-up to the election, and that unionized voters voted against the government in record numbers. While this article primarily assesses electoral impact, we offer brief perspective on the movement's impact on policy and politics in the conclusion.