In daily life, we are often confronted with choosing between tasks of different task difficulty. Diverse psychological theories suggest a direct link between task difficulty and motivation, namely a dynamic increase in motivation with increasing task difficulty. Here we test whether this is a reciprocal relationship: That is, does an increase in motivation bias participants’ decision in favor of the more difficult of two tasks? In a series of three voluntary task switching experiments, reward magnitude (low vs. high) was varied randomly between trials while participants could choose between an easy and a difficult task. Recent research has shown that a change in reward prospect is associated with a higher proportion of voluntary switches (Fröber & Dreisbach, 2016). Here we hypothesized that specifically an increase in reward prospect (resulting in increased motivation) should promote voluntary switches to the more difficult task. The results of all three experiments confirmed this prediction, suggesting that indeed the link between motivation and task difficulty can be exploited in order to trigger choosing a more effortful task. The results are discussed in light of recent theorizing on effort-based decision making.