In recent games City have conceded a costly penalty in Wednesday's Carling Cup semi-final exit at Liverpool and seen striker Mario Balotelli etrospectively banned for four matches for violent conduct for an offence not punished on field by the referee against Tottenham last weekend.
City have also had to deal without captain Vincent Kompany for four matches after a controversial sending-off, and Mancini said: "I think playing a lot of games is also difficult for them (referees). The refs sometimes are tired - to play every two or three days is difficult for the players, and for the referee. The referee is like me, like the players. They can be tired sometimes."
Mancini, however, does not think his team are the victims of any conspiracy, only bad luck.
He said: "Yes, yes - in December and January, it is only this way."
Defender Micah Richards, who conceded the penalty at Anfield for handball when the ball rebounded off his foot on to his arm, also believes City have had more than their fair share of bad decisions.
The 23-year-old suggests the club's now prominent position, as Barclays Premier League leaders, might be costing them the benefit of any doubt.
Richards said: "I wouldn't say everyone is against us, but when a team comes from nowhere and is doing so well, top of the league, you are going to get decisions against you.
"We don't think everyone is against us. We have coped well getting this far in the season, and you could argue some decisions could have been dealt with better but we can't dwell on them."