Sir Alex Ferguson has joked there would be a House of Commons inquiry if Manchester United got as many penalties as their "biggest threat" Manchester City.
The number of penalties City get at home has been the subject of debate for the past two years with them being awarded 21 since the start of 2010/11.
City have been awarded four in their past three games at the Etihad Stadium, two against Aston Villa and one each in the draws with Real Madrid and Everton.
And, ahead of United's Premier League trip to City on Sunday, Ferguson raised the issue as he admitted their nearest neighbours are now their closest rivals.
"The number of penalty kicks they get - 21 in the last year or something like that," said Ferguson.
"If we got that number of penalty kicks there'd be an inquiry in the House of Commons. There'd be a protest."
"Liverpool and United games over the last 25 years have been unbelievable," added Ferguson.
"They've always been the most important games. It's shifted because at this moment Liverpool aren't challenging for the league like City are.
"City are our biggest threat and we're their biggest threat, so that's changed.
"Their fortunes changed the minute Sheikh Mansour took over. We know the minute that happened it was going to be a different ball game altogether.
"But, as we have in the past, we have to accept their challenge like we did when Chelsea came along and when Arsenal overtook Liverpool in the early 90s. We have to do it again."
Don't miss any live and exclusive football coverage this festive season. Click here to visit Sky Sports' Festive Calendar
What will be the outcome in the match Man City vs Man Utd?