In the debate surrounding genetically modified (GM) food, intense controversies pertain over whether, or how, GM food products ought to be labelled. This paper examines how the GM-supportive and GM-sceptical alliances use arguments regarding labelling so as to strengthen their respective positions. It is an examination of conflicting arguments across social coalitions, corporations and policy-makers, mainly in the USA, but with certain European comparisons. The empirical material consists of written statements by the different groups. The paper suggests that the ideological and epistemological tenets are radically transformed, or even 'crossed over', between GM proponents and opponents when the focus is moved from GM per se to labelling. Two types of crossovers are identified: (i) the crossover of ideologies, and (ii) the crossover of epistemologies. The paper concludes that, while implementing mandatory GM labelling may have several democratic advantages, it is more urgent that both alliances become more reflexive and communicative concerning inconsistent or eclectic crossovers - both ideological and epistemological.