Recent studies have demonstrated that keeping an instructed task-set in working memory (WM) for prospective use can interfere with behavior on an intervening task that employs shared stimuli – the prospective task-set interference effect. One open question is whether people have strategic control over prospective task-set interference based on their expectations of whether task instructions will have to be implemented or recalled. To answer this question, we conducted two experiments that varied the likelihood with which a set of prospective task instructions would have to be implemented or recalled. Based on the hypothesis that participants are able to strategically modulate the manner in which a prospective task-set is encoded in WM, we predicted that as the frequency of implementing task instructions increased, so too would the magnitude of the prospective task-set interference effect. We found that task instructions held in WM caused significant task-set interference, even in mostly recall conditions, but – crucially – that this interference effect scaled positively with the likelihood of having to implement the prospective set. These data suggest that task instructions are obligatorily encoded as a procedural task-set, but that the degree to which this set impinges on ongoing stimulus processing is subject to some strategic control, possibly via modulation of the associations between declarative and procedural WM contents.