The RFU have issued warnings to Leicester Director of Rugby Richard Cockerill and Harlequins counterpart Conor O'Shea over their criticism of referees.
The pair have received letters from the authorities regarding comments made in the wake of Aviva Premiership clashes against Gloucester and London Welsh respectively.
An RFU statement said: "We have urged both directors of rugby to use the existing agreed feedback process and reminded them that questioning the integrity of referees in future may lead to their being charged with bringing the game into disrepute under RFU Rule 5.12."
Cockerill was left furious over the performance of Andrew Small during the Tigers' 17-12 win over the Cherry-and-Whites in late December.
He said: "I am lost for words. I have spent 30 years in the middle of scrums. I coach it every day. He [Small] needs to look at it and see his faults and try and improve. That's the whole point of coaching, whether you are a referee or a rugby coach.
"Guessing is the word I'd use and it's not good enough. Big games decide championships and European spots. You have to get it right."
O'Shea was similarly incensed by the efforts of Llyr ApGeraint-Roberts during last weekend's narrow 31-26 win at Welsh, saying: "Everything was wrong - it was incredible. The offside line was irrelevant, trailing runners coming back was irrelevant, backing into the maul, not releasing in the tackle - all irrelevant."
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