The present study investigated the production of the speech act of disagreement among Tunisian non-native students of English and American native speakers of English. Discourse completion test (DCT) was used to elicit disagreement strategies by the informants. Non-native informants produced a total of 376 acts and native informants produced 395 acts. The acts were categorized based on Brown and Levinson's (1987) Politeness Model. The speakers' performance of disagreement in variation with the contextual factors of Social Distance and Social Power was examined. Data was analyzed quantitatively and qualitatively. Results showed that there were significant differences between native and non-native speakers of English with regard to the frequency of direct and indirect strategies of disagreement. Non-native informants used a higher percentage of direct strategies (47%) and a lower percentage of indirect strategies (13%) than their native counterparts, who produced indirect strategies considerably (30%). NNSE opting for direct disagreement strategies might be attributed to their poor pragmatic and sociolinguistic knowledge of indirect strategies. This work can have pedagogical implications in teaching speech acts and pragmatics.