This paper examines transportation infrastructure in the Japanese empire and its role in positioning Korean migrants in the labor markets of the metropole. To do so, it focuses on the Pusan–Shimonoseki ferry which, between 1905 and 1945, transferred over 30 million people between Japan and Korea. During this time, the ships that comprised this ferry line helped articulate new borders between the metropole and its annexed colony. In this capacity, the vessels helped constitute and control the flow of a new class of colonial migrants as they entered the labor markets of Japan. Historically, transportation networks have been looked on as modes of conveyance or as symbols of political amalgamation. Colonial era descriptions of the Pusan-Shimonoseki ferry commonly maintained this view. However, rather than stress the spatial integration brought by the line, this paper highlights its function as a source of delineation. The ferries connecting Japan to its closest colony not only served as a conduit for Korean workers, but also introduced forms of constraint and contingency that shaped their ability to sell their labor in Japan. Transportation thus became an issue of political contestation and resistance. Korean workers and union activists employed an array of tactics to undermine the borders imposed through the regulation of transportation. Doing so was part of an attempt to assert greater control over the migrant's position in regional markets and mitigate the unevenness of the colonial system.