Agricultural guest workers have organized in recent years, but building viable unions to represent guest workers is challenging. To effectively represent guest workers, a union must address problems throughout the work cycle in both home and host countries. The Farm Labor Organizing Committee (FLOC) is one union that has organized guest-worker units in recent years. FLOC is experimenting with outreach, education, and representation activities in Mexico, the home country for members of their guest-worker bargaining unit. To be successful, FLOC and other guest-worker unions must use the advantages available in each country's legal and political regimes to advance the interests of its members. In Mexico, legal requirements for an employment relationship and restrictions on foreign union officials might stand in the way of union recognition. Neither is insuperable in principle, but they point to the legal and political minefield into which a guest-worker union might fall. Nevertheless, experiments aimed at developing new transnational forms and tools is a worthwhile venture because purely domestic forms of organization will not adequately serve workers in a world where both labor and capital cross borders.