In the post-Soviet neighbourhood, the European Union and the Eurasian Economic Union both address the common governance challenges, but there has been no institutional-level cooperation between the two unions. This total lack of cooperation on common regional challenges stands in stark contrast to the propositions of (neo-)functionalist/ rational institutionalist theories, which predict that technical cooperation can emerge even among actors who are hostile to each other. This article advances a social constructivist explanation to this puzzling phenomenon of noncooperation and argues that actors entrapped in normative conflicts are likely to refuse functional cooperation even when there are potential mutual gains.