Premier League referees have been reminded not to make direct contact with managers after Mark Halsey revealed he rang former Manchester United boss Sir Alex Ferguson last season.
Halsey, who retired from refereeing at the end of the 2012-13 campaign, has, in his book 'Added Time', claimed to have had a good relationship with Ferguson.
The ex-official has revealed how he contacted Ferguson to ask the Scot to support referee Mark Clattenburg, amid allegations that he had racially abused Chelsea's John Obi Mikel -- of which he was ultimately cleared.
In The Sun on Sunday, Halsey also alleged that Mikel said "I'm going to break your legs" to Clattenburg, and the threat led to referees considering a strike.
The Daily Mirror quotes Halsey as writing in his book: "I took matters in my own hands and rang Sir Alex asking him to speak out.
"He agreed and used his Friday press conference to say he could not conceive of Mark saying such things. It helped the situation a great deal.
"It took time to gain Sir Alex Ferguson's respect but in the end we had a very good relationship.
"One thing should be made clear about my relationship with Sir Alex. I may have spoken to him a lot and shared texts but he knew when I crossed that white line there were no favours.
"Players and managers would not respect you if you gave decisions based on friendship."
But the Professional Game Match Officials Limited, which provides match officials for all Professional Football matches played in England, has warned referees against such behaviour.
A spokesman said: "At the beginning of the season all our referees were reminded of the importance of adhering to the PGMOL protocols.
"This covers a number of issues, including making direct contact with managers and players, which for integrity reasons is prohibited.
"Any new publicity will only heighten awareness of adhering to these important PGMOL guidelines."