The MLBPA has offered to represent minor league baseball players. Union authorization cards will be distributed. If 30% of the players sign them, then here will be a formal vote. Majority rules at that point, and (if the players vote to unionize under the MLBPA umbrella) the National Labor Relations Board will require MLB/MiLB to recognize it. From that point on, the MLBPA would collectively bargain for MiLB players.
MLB has been under increasing pressure to improve pay and quality of life for minor leaguers. Over the past couple years, the players have had pay increases and housing provided. However, most still do not earn a living wage, and they are paid only during the season although they must train year round. Congress has even threatened to revisit baseball’s antitrust exemption status if things do not change.
Simply providing a living wage to the minor league players would be a relatively minor outlay by the major league owners and not worth the blowback that would be inevitable from any work stoppage. Thus, I expect the players’ vote to go the MLBPA’s way, and then for the minor league player to receive concessions fairly rapidly, concessions that should have been made decades ago.
There is one other aspect to this that I’ve not seen brought up: in recent collective bargaining agreements between the major league players and owners, minor league players’ rights often got negotiated away. These have included agreeing to fewer teams (and thus fewer jobs in affiliated baseball), fewer rounds to the draft, salary caps for the draft. If the minor leaguers are also MLBPA members, they would have some right to be heard within the union too, and thus might be less likely to have their benefits negotiated away by their major league brethren.