--- - |2 Abstract This article uses a discussion of struggles over attempts by the National Union of Seamen to exclude seafarers from the maritime labour market in the inter‐war period to contribute to debates at the intersection of maritime spaces and transnational labour geographies (cf. Balachandran 2012; Høgsbjerg 2013). By focusing on struggles engendered by the British Shipping (Assistance) Act of 1935, I explore some of the transnational dynamics through which racialized forms of trade unionism were contested. I argue that the political trajectories, solidarities and organizing spaces constructed by the alliances formed to oppose the effects of the act shaped articulations of ‘decolonization from below’ (James 2015). In this way, engaging with the political trajectories and activities of activists from organizations like the Colonial Seamen's Association can reveal new ways of understanding the spatial politics of decolonization and new accounts of who or how such processes were articulated and contested. I conclude the article by arguing that engagement with these struggles can help assert the importance of forms of subaltern agency in shaping processes of decolonization. - 'Global Networks, Volume 19, Issue 4, Page 539-562, October 2019. '