Questionable authorship practices in scientific publishing are detrimental to research quality and management. The existing literature dealing with the prevalence, and perceptions, of such practices has focused on the medical sciences, and on experienced researchers. In contrast, this study investigated how younger researchers (PhD students) from across the faculties view fair authorship attribution, their experience with granting guest authorships to more powerful researchers and their reasons for doing so. Data for the study were collected in a survey of European PhD students. The final dataset included 1,336 participants from five European countries (Denmark, Hungary, Ireland, Portugal, and Switzerland) representing all major disciplines. Approximately three in ten reported that they had granted at least one guest authorship to “a person in power”. Half of these indicated that they had done so because they had been told to do so by the person in power. Participants from the medical, natural and technical sciences were much more likely to state that they had granted a guest authorship than those from other faculties. We identified four general views about what is sufficient for co-authorship. There were two dominant views. The first (inclusive view) considered a broad range of contributions to merit co-authorship. The second (strongly writing-oriented) emphasised that co-authors must have written a piece of the manuscript text. The inclusive view dominated in the natural, technical, and medical sciences. Participants from other faculties were more evenly distributed between the inclusive and writing oriented view. Those with an inclusive view were most likely to indicate that they have granted a guest authorship. According to the experiences of our participants, questionable authorship practices are prevalent among early-career researchers, and they appear to be reinforced through a combination of coercive power relations and dominant norms in some research cultures, particularly in the natural, technical, and medical sciences.