Entering Monday's action, Pena is hitting .219 with five RBIs, and he has been vulnerable to breaking balls.
"[Pena] has been working with [hitting coach] Lenny [Harris]," Acta said, "and making sure that he lays off the ones that are off the plate. He is going through a struggle like a lot of the guys here right now."
Bill Ladson is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.