This article presents an interdisciplinary analysis of discourses on refugees, asylum seekers, immigrants, and migrants (RASIM) in mainstream and alternative media in the Czech Republic. Using techniques from corpus linguistics (CL) and natural language processing (NLP) and drawing on insights from media sociology, we demonstrate the value of an interdisciplinary approach for conducting robust research that can inform policymakers and media practitioners. Our analysis of nearly one million documents from January 2015 to February 2023 reveals distinctive terms and phrases used by alternative media, highlighting the growing divergence between the mainstream and alternative media discourse and its intensity over different periods. These findings have implications for understanding the mobilization of anti-systemic groups, particularly those on the far right.