You do have multiple employers, and a single union can represent workers across an industry, not just at 1 employer. Having multiple unions would remove the mon

You do have multiple employers, and a single union can represent workers across an industry, not just at 1 employer. Having multiple unions would remove the monopoly power unions enjoy, but a triopoly is still pretty powerfull, and reduces the risk of corruption. Of course, if the triopoly was enforced by statute, then a corrupt member could act with impunity knowing that it cannot loose too much of its power.