When scholars study business power, they usually focus on big business. Small and medium-sized enterprises (SMEs), which comprise the vast majority of companies, are therefore excluded. The article looks at how Finnish SMEs have defended their interests in an increasingly corporatist country. It focuses especially on how they have managed to resolve the collective action problem, which prior theoretical studies have identified as a major issue in the heterogonous SME sector. We find that one association managed to build ‘a movement’ by underlining common threats to SMEs. We also assess the steps taken by other, smaller and less populist SME associations, arguing that that such diversity has brought some benefits, as competing associations have employed different tactics and been active in separate arenas. This article is based on the archives of SME associations and other business associations as well as earlier research, memoirs, other published works and newspaper articles.