I sent an email to the MLBPA about grooming policies and how the union viewed them. They said that although the aren't part of the CBA, they have no issue with such policies as long as they are within reason. They haven't had a reason to view them as an issue for collective bargaining.
the player contract says
"The Club shall be permitted to deduct
from the Player’s salary only those amounts that are specifically
authorized by the Basic Agreement, this contract, any mutually agreed
upon special covenant hereto, or a separate authorization signed by the
so if a player doesn't want to pay the fine, they can just not pay