If the player's union have concerns about how the owners are using the minor league system, then the leagues could adopt the same contract structure as the NHL. A NHL player can sign either 1-way or 2-way contract. If he signs a 2-way contract, then he is giving the NHL team the right to call him up/send him down to the minor league affiliate as much as desired. If he signs a 1-way contract and the NHL team wants to send him down to the minor league, then he must clear waivers before the transaction is completed. If another team picks him up off waivers, then his current team has the right to match any new offers to retain him or refuse to match and let him sign with the new team. I believe his old team gets some form of compensation (i.e. in the form of salary cap relief) for him not clearing waivers.