Whereas the automaticity of emotion processing has been investigated in several cognitive domains, its mandatory influence on cooperative decisionmaking is still unexplored. We employed an interference-task to evaluate whether explicit instructions to ignore the emotions of others during alleged interpersonal interactions override their behavioral effects. Participants played a Trust Game multiple times with eight cooperative or noncooperative partners, who displayed facial expressions of happiness or anger. Emotions were non-predictive regarding the partners’ cooperation. In Experiments 1 and 2 participants were explicitly asked to ignore the emotions, and the uncertainty about the partners’ behavior varied. We found an effect of emotional interference; whereas happy partners speeded cooperative decisions, angry ones speeded non-cooperative choices. This was replicated in Experiment 3, where the request of ignoring emotions was removed. Our results show the inevitable influence of the emotional displays of others during cooperation decisions, which fits with theories that contend for a tight link between emotions and social context.