Blackwell was unhappy with Dean earlier this season after he harshly sent off Blades defender Matthew Kilgallon in the Sheffield derby at Hillsborough.
The Blades boss believes handing Dean such a high-profile game puts the official under undue pressure.
"It's not fair on him, me or the club," fumed Blackwell. "Our last meeting was less than amicable and I marked him exceptionally low and yet now he turns up for our biggest game, the biggest club game in the world.
"What will happen if he makes a cock-up on Monday? I'm amazed at the stupidity of it. I'm very, very angry about people who run the game not using their common sense and putting Mike Dean in what could be a very embarrassing position.
"It puts him under pressure. We're going to go to Wembley with 40,000 Sheffield United fans knowing his last performance cost us a result at Hillsborough screaming down his neck.
"That's not fair on Mike Dean or me. There are four or five top referees they could have given the game to. It's a situation they didn't need to create."
Source: Team_Talk