Major League Baseball is requiring players to be vaccinated against COVID-19 in order to participate in the Arizona Fall League, reports Nick Piecoro of the Arizona Republic. It marks the first instance of an MLB vaccination mandate directly affecting players.

Last week, Ken Rosenthal of the Athletic reported that MLB was mandating vaccinations among non-playing team personnel in order for those individuals to be granted access to the field during postseason play. That requirement did not apply to players, as any sort of vaccine mandate for MLB players would need to be agreed upon with the Players Association. MLB can and has attempted to encourage vaccinations among big leaguers by loosening health and safety protocols for teams that fully vaccinate 85% of Tier 1 personnel.

The Arizona Fall League is an annual prospect showcase that takes place after the conclusion of the standard minor league season. It is operated by MLB. Teams send a contingent of players at various minor league levels to the AFL in order to log extra playing time. The caliber of player assigned to the league is also highly variable, but it’s not uncommon to see at least a few of the league’s most promising prospects participate.

It’s possible a few players on MLB 40-man rosters will be tabbed for Fall League action. Those players are members of the MLBPA, but Piecoro notes that the Fall League is generally treated as a minor league, making a MLB vaccination mandate for players permissible. That naturally raises the question whether MLB could consider a vaccination mandate for all affiliated minor leagues next season even if the MLBPA doesn’t agree to a mandate at the big league level. There’s no indication that’s presently the league’s intent, but one executive opined to Piecoro the Fall League vaccine mandate might wind up being a precursor to similar measures for minor leaguers during next year’s Spring Training.