If the weight of trade unions is an important contextual variable in terms of diversity management, the impact of union membership itself is less known. Based on the 2008-2009 ESS survey requested by the European Commission and conducted among 48,141 people in 25 European countries, this study aims to assess the negative impact of union membership on ageism towards the elderly. Although union membership in the countries of Northern Europe is often explained by the material benefits which it opens up, it further reduces ageism in these countries compared to other European countries.