Manager Mark Robson felt the decision to send Graham Stack off and award a penalty influenced Barnet's 2-1 loss at Fleetwood.
The Bees were leading 1-0, courtesy of Jake Hyde's fifth-minute opener, when Stack was given his marching orders for upending David Ball in the box in the 24th minute.
Ball converted the penalty before on-loan Blackpool midfielder Tom Barkhuizen headed in the winner for Fleetwood.
Robson said: "The lads weren't sure if it was offside or not. If that's given offside then it's a free-kick to us. As it is, he's got in, the lad's brought him down and the rules are that Stack has to go. It's a major disappointment.
"We started well after putting in a really good performance last weekend and really thought we could get something out of the game.
"I felt we were just starting to come together, unfortunately we lose a man after 25 minutes and it's all happened from there."
Update:
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