Professionals' trade union Prospect, who represent referees, have urged the Football Association to "grab the nettle" and take firm action against Sir Alex Ferguson following his comments about Alan Wiley.
The FA have written to Manchester United manager Ferguson to ask him to explain his claim 49-year-old referee Wiley was "not fit" after taking charge of his side's 2-2 draw with Sunderland at Old Trafford on Saturday.
Alan Leighton, the national secretary of Prospect, told BBC Radio 5 Live's Victoria Derbyshire programme the FA must act to protect the Respect campaign.
Leighton claimed a fine or touchline ban for Ferguson may have little impact, and suggested the FA take action that would have a greater effect.
Leighton said: "I don't know what Sir Alex earns but a small fine or a touchline suspension would be like water off a duck's back to him so I think there has to be some recognition that this is a serious allegation that needs to be properly dealt with and punished severely.
"There are issues around suspension from the job, that would be new territory that hasn't happened before but I think the FA has to grab the nettle on this one.
"Because a small fine or a large fine would be like water off a duck's back, there has to be some sort of punishment that is going to stop people from doing this or otherwise we are going to see more and more of it.We have to be talking about punishments that are going to really lead to a change in behaviour."
Leighton stressed: "I think the FA has to act on this, I think there is no future with the Respect campaign if the FA don't act. I see the FA have asked him to explain his comments, I'm not really sure what requires explanation.
"I think his comments were fairly clear so I think at this stage I would like to see the FA act and act quickly to restore Alan's reputation and ensure that referees are going to get some protection from what seems to be a growing approach that managers feel they can abuse them."
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