[fallingfrog]

From the point of view of an employer, the easiest way to crush a union is to pay all employees according to the union contract even if they're not members of the union. That way, there's no incentive to join. So the way the union will combat that loophole is to specify in the contract that the employer agrees to only hire union labor or to charge agency fees to anyone that is paid according to the union rate. "Right to work" laws just make those kinds of agreements illegal.