I did three rounds of background interviews with active trade unionists, which I used both as a source of general information on the subject matter of strikes, and to learn about specific disputes. The first round took place in May 2012 and formed part of a research project I carried out with my colleague Jörg Nowak on political strikes against austerity, which was funded by the Rosa Luxemburg Foundation. Edited versions of the interviews were published in the book Politische Streiks im Europa der Krise [Political Strikes in the European Crisis, Hamburg, 2012] that I co- edited with Jörg Nowak and Florian Wilde. This project constituted the starting point of my research on strikes. Since these interviews are in the public domain anyway, there is no need for me to use pseudonyms. The interviewees were:

• • Sabin del Bado, LAB, Basque Country, Spain

• • Felipe Van Keirsbilck, National Centre of Employees [Centrale Nationale des Employés], Belgium

• • Olga Karyoti, Association of Translators, Editors, Copy- Editors [Σωματϵίο Μϵταϕραστών, Επιμϵƛητών Διορθωτών], Greece

• • Christine Lafont, Solidaires Union, France

• • Deolinda Martin, CGTP, Portugal

• • Nuria Montoya, CC.OO, Catalonia, Spain

• • Michael Pieber, Union of Private- Sector Employees Print Journalism Paper [Gewerkschaft der Privatangestellten Druck Journalismus Papier], Austria

• • Sean Vernell, UCU, Britain

In a second round, I discussed the state of unionism, the resistance against austerity and the social and political relevance of strikes in Britain with four trade unionists active in the country. At this point, I had not decided yet that I would zoom in on non-industrial strikes, which explains why one of my interviewees is active in the chemical industry. This second round took place in September and October 2015. These interviews have not been published and were not led with the intention of fully publishing them. To protect my sources, I use pseudonyms and do not disclose the exact geographical location of their workplaces and places of residence:

• • Ricardo Jameson, community organizer, Unite, Southeast of England

• • Thomas Hunter, shop steward in the chemical industry, Unite, Northwest of England

• • Timothy Mackenzie, head of a branch of the PCS, Scotland

• • Laura Wilson, full- time official, Chartered Society of Physiotherapy, Midlands

In a third round, I interviewed four trade unionists representing the GDL in July 2018, who were actively involved in the strikes of 2014–15.