Two studies are reported using the theory of planned behaviour (TPB) to examine Koreans' intentions and self-reported behaviour of joining and not joining alcohol-related social gatherings with work colleagues after work hours. Study 1 showed that group-related attitudes and perceived behavioural control of the TPB components regarding joining were significantly associated with intentions to join. Study 2 examined TPB components regarding not joining and intentions to not join. Study 2 found that although none of the TPB components was directly related to intentions, subjective norms from work colleagues moderated the effect of group-related attitudes on intentions to not join. The TPB components and intentions were not significantly related to self-reported behaviour of joining. The findings indicate that the relationships between the TPB components and intentions can be different for engaging and not engaging in a behaviour.