Benitez was furious with the Austrian official for adding four minutes injury time at the end of Tuesday's Champions League semi-final clash, which eventually saw John Arne Riise put through his own net.
"He warned us to be calm and not be affected because he'd be favouring Chelsea.
"Rafa said Plautz had refereed six games in Europe this season before our game and FIVE times the home side failed to win.
"He reminded us he was particularly poor in our game with Marseille when we lost 1-0 at Anfield this season."
Plautz, 44, is rated by UEFA as one of their top officials and is one of 12 refs for the Euro 2008 finals.
Benitez said: "There were 94 or 95 minutes and every decision went against us.
"It's not the first time. We knew before the game it was going to be difficult with him."