On December 31, 2020, The National Science Library of the Chinese Academy of Sciences (CAS) released a list of 65 international scientific journals, all of them indexed by the Web of Science, that were said to be potentially in conflict with academic rigour. The list immediately influenced the publication patterns of Chinese researchers. A year later, on December 31, 2021, CAS released a revised and reduced list of 35 questionable journals and said the publishers in the meantime had reacted constructively and improved the procedures of their journals. This study aims to provide an understanding of the motivations and criteria behind the list, partly by reviewing Chinese policy documents and public debates, partly with a quantitative analysis to detect the relative importance of the criteria used to select the journals for the list.