Instant messenger is being rapidly deployed in the workplace. Current studies largely focus on the adoption of IM and how IM is used. Little research has been conducted to understand the potential impact of using IM in the workplace. This paper contributes to the literature on Instant Messaging by theorizing how some technological features of IM could intertwine with social characteristics and jointly influence user task performance and perceived workload We hypothesize that the effect of interruption on task completion time is likely to be dependent upon the hierarchy level of message sender and that interruptions from a supervisor aggravate the negative impact of interruptions on task quality.