He was expecting a flag on Cowboys cornerback Terence Newman, who tossed him out of bounds moments after a blown whistle. Smith argued for a late hit, then put his arms around an official, which led to a 15-yard unsportsmanlike penalty and automatic ejection.
The 24-20 loss to the Cowboys cost the Panthers a chance to clinch a playoff berth.
Smith, who has developed into Carolina's most reliable receiver, has compiled 1,432 yards and 11 touchdowns on 94 receptions this season. After the game, he admitted he was wrong.
"You are not supposed to touch the ref. I understand that," he said. "I wasn't doing it to put him down or anything like that. I put my hand on his back. It was a gesture."