Focusing on the effects of union membership on partisan preferences, this article

explores how changes in Swedish industrial relations and trade-union politics have

affected electoral support for Left parties since the mid-1980s. Our analysis shows

that unionization among blue-collar workers has declined sharply since the mid-

1990 and that this development has contributed to the decline of electoral support

for the Social Democrats and for the Swedish Left as a whole. In addition, we find

that the association between union membership and voting for Left parties has declined

among white-collar employees without tertiary education as well as bluecollar

workers over the same period. We argue that sectoral blue-collar and whitecollar

unions alike have responded to membership losses and intensified competition

between unions by engaging in practices that render the partisan preferences

of union members less distinctive than what they used to be (less Left-leaning relative

to non-unionized counterparts).