Abstract Unparliamentary language is an element of parliamentary discourse. It is the language ruled or signalled to be out of order or likely to cause disorder by the presiding officer of a legislative chamber. This article aims to explain why a specific subset of New Zealand parliamentarians – identified as the ‘principal users’ of unparliamentary language – repeatedly used language that was contrary to the institutional rules. The discussion draws on the Community of Practice framework developed by Etienne Wenger with a focus on the concept of ‘power’. Beginning at 1890, when the party system was established in the New Zealand House of Representatives, the research this article draws on recorded each identifiable example of unparliamentary language over the next sixty years. It was found that four periods as defined by differences in the typical characteristics of users of unparliamentary language emerged: mavericks, loners and bullies, 1891 to 1906; the early socialists, 1906 to 1928; the rise of the New Zealand Labour Party, 1928 to 1935 and full cross-party participation, 1935 to 1949. Parallels with historical research on disorder in the British House of Commons are drawn. The results show the ‘principal users’ of unparliamentary language used linguistic rule breaking to exert a form of ‘power’ over individuals and the institution.