The penalty was supposed to go into effect for Monday night's game at Texas, but Willingham appealed. He can keep playing until the appeal process is complete.
Willingham, who was hitting .225 while leading the Athletics with five home runs and 17 RBIs, was in the starting lineup batting fourth against the Rangers.
Major League Baseball also fined Willingham an undisclosed amount.
Willingham was ejected by umpire Bill Miller for arguing a called third strike in Saturday night's game at Kansas City. Willingham made contact with Miller during the eighth-inning disagreement.
"He informed me what they told him, he's appealing it, and I back him," Oakland manager Bob Geren said. "It's his decision. Either way. My players, I'm always going to back 'em, support any decision they make."
Geren wouldn't elaborate.