A large literature argues that public opinion is vulnerable to various types of framing and cue effects. However, we lack evidence on whether existing findings, which are typically based on lab experiments involving low-salience issues, travel to salient and contentious political issues in real-world voting situations. We examine the relative importance of issue frames, partisan cues, and their interaction for opinion formation using a survey experiment conducted around a highly politicized referendum on immigration policy in Switzerland. We find that voters responded to frames and cues, regardless of their direction, by increasing support for the position that is in line with their pre-existing partisan attachment. This reinforcement effect was most visible among low knowledgeable voters that identified with the party that owned the issue. These results support some of the previous findings in the political communication literature, but at the same time also point toward possible limits to framing effects in the context of salient and contested policy issues.