Preferential voting in a proportional list system is an essential means by which voters can significantly influence which particular politician will represent them. However, preferential voting takes on a new dimension when several parties run on the same list as a coalition. In this case, the intra-party competition may become inter-party competition, where one or more parties may gain significantly from preferential voting at the expense of their partners. Despite this, research on this topic has been significantly neglected. Using the case of the 2021 Czech general election, where two newly formed electoral coalitions (SPOLU and PIRSTAN) run, we examine the nature of preferential voting in this different context of electoral coalitions. In the first part of the analysis, when we analyzed the characteristics of all candidates of both coalitions, we first confirmed that the candidate effect commonly observed in the case of conventional candidate lists also exists in this context. At the same time, we found that the candidate effect (through the adequate distribution of influential characteristics across parties in a coalition) can also affect the inter-party competition (as was the case of the PIRSTAN coalition). In the second part of the analysis, we found that in the context of electoral coalitions, party characteristics can also have a substantial effect on preferential voting (as was the case of the SPOLU coalition). Thus, both of these categories of effects can exist in the case of coalition lists, and both can affect inter-party competition. Nevertheless, future research is needed to confirm whether these findings are generally valid or whether the Czech case is somehow deviant. Existing research on this topic does not allow for a comparison.