Disagreement has been relatively less studied than other speech acts such as requests or compliments, especially as produced by nonnative speakers of English. The present study aims to analyze the production of disagreement by an international group of Master students who use English as lingua franca in an online collaborative project. More specifically, the study tries to answer the following research questions: (1) does linguistic proficiency entail pragmatic competence? and (2), what is the effect of explicit instruction on pragmatic competence? To this purpose, two subcorpora (prior to and post instruction) were gathered by means of two online collaborative activities, rendering a total of 25,347 words. The analysis of the data reveals that high linguistic proficiency plays a crucial role in pragmatic competence. On the other hand, explicit instruction seems to benefit students to different extents, with intermediate B1 students improving their expression of disagreement and lower level students still remaining far from pragmatic and linguistic competence.