Never thought of consolidation as increasing market power to set wages against labor but once you put it this way, the conclusion is quite obvious.
E: That said, consolidation in the presence of unions should increase the power of said unions because few or even a single union could bring down a whole business sector. E.g. if ROBeLUS was a single unionized company, its union could halt telecommunications via strike action. There would be no other potentially ununionized company to "step in" and fill the gap.