United players have picked up 15 yellow cards and one red so far this season.
“We’ve had two of our toughest away games in a row, at Liverpool and Chelsea,” Ferguson told the Daily Mirror.
“It’s very difficult for a referee at Liverpool, as we all know.”
Seven of their yellow cards came in their clash with Chelsea.
Fergie continued: “And if you analyse the Chelsea game there wasn’t a bad tackle in the match.
“So I’ve no problem with the discipline of my team, none at all. We always try to play our football, play the right way and that’s the way we will continue.”