This paper analyzes the determinants of bargained wage differences at firm-level in Asturias. First, a theoretical model is describedto identify these factors. Second, this model is estimated using a panel of five years that contains information about the firms from Asturias that have bargained their own collective agreement. This kind of firms are chosen to know the level of bargained wage rates set up in their collective agreements. Estimations show that sales per employee, number of bargained hours of work, replacement ratio, union power, some financial variables, profits per employee and skill-mix, are the main determinants of bargained wages. Finally, the estimated insider weight is 0.22. This value is greater than the former ones estimated for the Spanish case, probably because of  the special features of the current sample.