This paper explores the relationship between communism and Tunisian nationalism in the Gafsa phosphate mines, from the acceleration in strikes against the mining company in the late 1940s to the early 1960s. The rise of Tunisia’s phosphate industry in the late 1890s attracted workers from around the Mediterranean – particularly from Italy, France, Algeria, Libya, and Morocco – to meet the French-owned Gafsa Phosphate and Railway Company’s demand for cheap labor. This transnational labor diaspora brought to Gafsa leftist ideas and techniques of resistance that circulated around the Mediterranean basin during the late-nineteenth and early-twentieth centuries. As these ideas and techniques interacted with local practices of anti-colonial resistance while confronting the reality of racial discrimination in the workplace, debates arose over the possibilities and limits of transnational labor solidarity in the Gafsa mines. In the 1940s, these debates became particularly salient when the Union générale tunisienne du travail (UGTT) broke from the communist-led Confédération générale du travail (CGT) to organize Tunisian workers on a national basis. By documenting the history of collaboration and competition between communist and Tunisian nationalist unions in the Gafsa mining basin, I argue that the UGTT’s post-independence emergence as Tunisia’s dominant labor organization was not inevitable, and that the political engagement of Gafsa’s Maghribi and European workers played a decisive role in the processes that led to this outcome. I draw on Gafsa Phosphate and Railway Company records, documents generated by Gafsa’s labor unions, oral histories of Gafsa miners who were active in the anti-colonial resistance, French military and security documents, newspapers, and colonial and post-independence administrative records housed in both Tunisia and France. This paper contributes to a growing body of literature on the role of labor contestations in nationalist movements while also challenging dominant paradigms in Tunisian nationalist and Western historiography, which center on the political and social elite in Tunis. Instead, I argue that outcomes in Gafsa were determined by local actors operating within the context of both national and transnational leftist movements. I show how Gafsa’s residents imagined alternate visions for Tunisia’s political economy that played a decisive role in the 1940s and 1950s, even as these possibilities did not materialize in the 1960s. Nationalist histories – not only of Tunisia but also of other post-colonial states – have elided these divisions and contestations, yet they are essential for understanding the processes by which the post-independence nation was constructed.