Local government amalgamations may have unintended consequences on electoral behaviour. Using the most recent local elections in Denmark as its case, this article demonstrates that inter‐level split‐ticket voting between three levels (national, regional and local) decreased slightly from 2001 to 2005 – that is, simultaneously with the implementation of a major reform, where many municipalities and all the counties were amalgamated. These amalgamations affect the level of split voting through a process where the local party system operates as an intervening variable: the larger municipalities have a more nationalised local party system, which leads to fewer voters being vote splitters by necessity. The analyses combine general electoral statistics with large voter surveys and benefit from the quasi‐experimental setting offered by the fact that not all municipalities were amalgamated.