Karl Marx had to deal with a situation that bears an uncanny resemblance to the current predicament of trade unions regarding immigrant workers. The First International faced the threat of an internal division along ethnic and national lines around the Irish question, and more specifically around the role played by Irish immigrants in England. Firstly, I will argue that Marx’s late work on Ireland, and especially his change of opinion on its tactical importance, cannot be isolated from his vigorous manoeuvring within the International to prevent an internal rift over the question of immigrant workers. Secondly, I will contend that Marx’s theoretical contribution on the Irish question fails to consider that class politics are not only international in nature, but also transnational. Consequently, Marx overlooks the tactical importance of immigrant workers who could play a pivotal role in challenging exploitative and oppressive ties on the international scene.