West Ham United boss Sam Allardyce feels refs are suffering from fatigue.
Allardyce blames the lack of numbers for their poor decisions at this stage of the season.
He said: "This is a difficult period for referees.
"Why do they always seem to make more wrong decisions now? It's probably because they are overworked and they are fatigued.
"The system has to be looked at and in my opinion it's because they are fatigued. Referees are travelling all over the country and out in Europe and have been since the start of the season.
"There's not enough of them. They try their very best to get things consistently right. But it happens every year around this time of year - the controversy.
"We had a couple in our last game and there have been many throughout football over the Christmas period.
"Fatigue is everything in terms of decision making. Once it kicks in you lose the ability to make those decisions correctly."