A tractor comprises a tractor frame, driven ground engaging means, and an electronic tractor controller. A baler comprises a baler frame coupled or connected to the tractor frame, a crop receiving means, a baling chamber, a bale size sensor associated with the baling chamber, and an electronic baler controller. The baler controller is operable to submit a halt signal to the tractor controller when a bale size signal provided by the bale size sensor indicates that a bale has reached a size equal to or exceeding a first predetermined size. A control method includes the baler controller generating a tractor halt signal in response to certain conditions of the baler system and the tractor controller preventing tractor motion in response to the halt signal. The method also includes, when the baler controller is generating the halt signal, enabling motion of the tractor if the operator issues a command for the tractor to move by manipulating the command device, and within a certain time period of said command being issued, the baler controller generates a tractor motion enabling signal in response a status of the baler system. The method further includes, when the baler controller is generating the halt signal, enabling motion of the tractor if the operator moves the tractor command device in a special manner.