An agricultural baler including a bale case having a wall portion with an opening for introducing crop material; a plunger disposed moving in the bale case to compact the crop material into bales; a duct for transporting the crop material to the entrance opening; and a stuffer unit operably associated with the duct and including a fork assembly. The stuffer unit includes tines and a drive mechanism acting on the fork assembly. The drive mechanism includes a first drive member configured for a reciprocating motion along a path of movement; a second drive member configured for a reciprocating motion along the path of movement of the first drive member and operatively connected to the fork assembly; and a selectively operable coupling arrangement configured for selectively coupling the second drive member either to the first drive member or to a stationary part of the baler.