Multinationals' aggressive tax lobbying that involves free-riding behaviour and results in disproportional benefits to the disadvantage of other taxpayers, is problematic for several reasons. Such lobbying undermines the legitimacy of tax legislation and has a negative impact on trust in the tax system. Based on Immanuel Kant's ethical theory, this article first suggests a new normative basis for a moral duty that requires multinationals and their leaders to be transparent about their political activities and tax lobbying. Next, it introduces a new concept of transparency in respect of tax lobbying. 'Deliberative transparency' requires multinationals and their leaders not only to be open about their reasons for tax lobbying, but also to deliberate with stakeholders and, maybe even more importantly, to provide evidence supporting their lobbying positions. Finally, based on these new understandings, additional government interventions against aggressive tax lobbying are suggested, for example mandatory stakeholder consultation, reporting on stakeholder attitudes and perception, and evidence-based lobbying requirements.