Engaging in comparative lobbying research is a challenging task, because public affairs is complex and highly context-dependent. Thus, qualitative case studies have been researchers' primary choice. However, the case method has been subject to much debate surrounding its rigor, in terms of reliability, internal validity, and generalizability, and particularly its potential for theory building. To propose a framework for researchers conducting lobbying case studies as well as for reviewers receiving such work, we apply a positivistic approach on case study rigor from management studies and expand the framework to tackle the specific challenges of comparative qualitative lobbying research. Thus, we expand the research framework by a set of variables specific to public affairs: We add enrichment for internal validity, contextuality, and comparability for external validity, interdisciplinarity for construct validity, and hypertextsearchable databases for reliability. Thereby, we aim to transfer the lessons learned from management studies in terms of rigorous qualitative case studies to public affairs to help build novel and explanatory theory in the field and to provide guidance to researchers how to design a rigorous case study.