The speech act of disagreement has been one of the speech acts that receives the least attention in the field of pragmatics. This study investigates the ways power relations influence politeness strategies in disagreement. In order to determine whether and to what extent the realization of the speech act of disagreeing and the of appropriate politeness strategies by Iranian EFL learners, in a university setting, across different proficiency levels (intermediate and upper-intermediate) differ in relation to people with different power status a Discourse Completion Test (DCT) was completed by 40 Iranian EFL learners who were placed at two different levels based on their scores on a proficiency test. The DTC consists of five scenarios in which the subjects are expected to disagree with two higher statuses, two with peers and one with a lower status. The selection of disagreement situations in DCT, borrowed from studies by Takahashi and Beebe (1993) and Liang Guodong and Han Jing (2005), were based on relative power and status of people. The taxonomy from Muntigl and Turnbull (1995) was employed for counting and analyzing the utterances of disagreement from the responses. The findings of this study provide some evidences for the relation between the learners' level of language proficiency and type and frequency of disagreement and choice of politeness strategies associated with people with different power status. In conclusion, it was argued that the results can be closely related to learning contexts and textbook contents. Finally some suggestions such as making learners aware of second language pragmatic rules and socio-cultural constraints on speech acts as well as grammatical rules in order to have a successful communication were put forward regarding the issue.