Planets

Official rule text

67.5 A player is limited by the number of units in their reinforcements. a If a player cannot produce a unit because it is not in their reinforcements, that player can remove a unit from any system that does not contain one of their command tokens and place that unit in their reinforcements. Then, that player can produce that unit. A player can remove any number of their units in this way; however, any units that are removed must be produced immediately. b When producing a fighter or infantry unit, a player can use a fighter or infantry token, as appropriate, from the supply instead of a plastic piece.