This thesis explores the incentives for trade unions §to coordinate their actions across borders in the §face of an increase in international product market §integration. Overall, the crucial role of the §strategic interactions between industrial relations §systems and the consequences of cross-country §asymmetries in economic and institutional conditions§are evidenced. The outcomes suggest that if §countries are symmetric trade liberalisation always §increases the incentives for unions to sign explicit §transnational collective bargaining agreements. In §the absence of binding contracts, however, unions' §willingness to collude may depend both on the degree §of product market integration and on the degree of §substitutability among traded goods. This thesis explores the incentives for trade unions §to coordinate their actions across borders in the §face of an increase in international product market §integration. Overall, the crucial role of the §strategic interactions between industrial relations §systems and the consequences of cross-country §asymmetries in economic and institutional conditions§are evidenced. The outcomes suggest that if §countries are symmetric trade liberalisation always §increases the incentives for unions to sign explicit §transnational collective bargaining agreements. In §the absence of binding contracts, however, unions'' §willingness to collude may depend both on the degree §of product market integration and on the degree of §substitutability among traded goods.