Since 2006 Chelsea have not lost a league game that Atkinson has refereed
By Dan Roan
BBC sports news correspondent
Sir Alex Ferguson should apologise for his "unacceptable" attack on referee Martin Atkinson, according to the trade union that represents match officials.
The Manchester United boss said he had "feared the worst" when Atkinson was appointed for the game at Chelsea.
"The simple way out of this is an explanation and an apology," Prospect head Alan Leighton told BBC Sport.
He was speaking before Ferguson was charged with improper conduct by the Football Association later on Thursday.
United's manager was furious that Chelsea central defender David Luiz was not shown a second yellow card for tripping striker Wayne Rooney on the edge of the Chelsea box.
Instead, Atkinson waved play on as Chelsea surged up the pitch before awarding a penalty when substitute Yuri Zhirkov tumbled to the ground under Chris Smalling's challenge. United went on to lose the Premier League match 2-1.
"You hope you get a really strong referee in games like this," said Ferguson afterwards.
"It was a major game for both clubs and you want a fair referee. You want a strong referee anyway and we didn't get that. I don't know why he's got the game. I must say that when I saw who was refereeing it, I feared the worst."
Atkinson has refereed 13 Premier League matches involving Chelsea since the 2006/07 season with the London side winning 12 and drawing one, including two victories over Manchester United and one over Liverpool.
But Leighton, Prospect's national secretary, said he was "surprised" by Ferguson's comments and pleaded with managers to be more guarded in their post-match media interviews.
I would call on all managers to be more careful about what they say
Alan Leighton Prospect national secretary
"The key word in this was the question of fairness, and the suggestion that Martin Atkinson, or indeed any other referee was unfair or biased, or favouring one side against another," said Leighton.
"It's that issue of integrity that's pretty fundamental to the game. The game only really exists on the basis it's fairly moderated and any suggestion that a referee in the Premier League is unable to carry out that job with integrity is fundamentally damaging to the game.
"It's not a question of whether there are charges. The damage is done. The issue is resolved a lot more quickly if Sir Alex does one small thing: apologise.
"I would call on all managers to be more careful about what they say."
Ferguson was previously charged with improper conduct for criticising Atkinson after United lost 1-0 to Portsmouth in an FA Cup quarter-final in 2008.
He was also fined £20,000, and handed a four-match ban, two of which were suspended, In October 2009 after he said referee Alan Wiley was not fit enough physically to officiate.
The suspended two-match ban would be automatically activated, on top of any new punishment, should Ferguson be found guilty of a similar charge before the end of this season.
"We've discussed in the past what an effective penalty is and there is experience of people being given stadium bans and that's got to be part of the armoury," added Leighton.
"In any judicial form you can't keep on giving the same penalty to a serial offender - I am being general now - if people re-offend the natural course is that the penalties get ratcheted up.
"The issue is that if you have a penalty that is so minor that people are quite happy to accept it and carry on, that's a system that doesn't necessarily work, but that's a much wider issue than the one we're talking about now."
Atkinson also refereed the corresponding fixture at Stamford Bridge last season and was criticised by Ferguson for awarding a free-kick, which the Scot believed should never have been given, allowing John Terry to score the winner in a 1-0 victory.
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