Collective Bargaining

Plants A and B both manufacture refrigerators and are located in the same state. The plants, however, are owned by different companies, Company A and Company B. Plant A is the only plant in Company A that manufactures refrigerators while in Company B there are a number of plants manufacturing refrigerators (including Plant B). Unionized employees in both plants are currently bargaining over a labor contract with the management of their respective companies. In what situations would the employees in Plant B have more bargaining power than employees in Plant A?