George works in a factory and is a member of the labor union. He thinks his wages are low for the work that he does, so he tells the union representative that his employer should increase his wages. The representative asks the other workers if they feel the same, and they all agree. The following week, the union representative met with the factory owner regarding an increase in wages, and the employer agreed to it. What strategy did the union use to get the owner to agree to increase wages?