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."
Gilbert has released a new line of rugby cleats. The Gilbert Virtuo 8S is part of the exciting new product. Check it out.
The entire All Blacks apparel line has been updated for 2013/14. Check out the New Zealand All Blacks polo.
The Nike Tiempo is a solid rugby cleat and one of few styles still made from full-grain natural leather.
The Gilbert Blitz 8S rugby cleat is a great cleat at a great price of $69.99. Get a new pair of cleats today.
A cool looking all black rugby cleat with the high performance adidas is known for. Get in the Gear!
Wear the crest of the British and Irish Lions on your t-shirt. A great look for the summer.
$29.99
The All Blacks Performance t-shirt is black with hints of blue from the training jersey. Very Cool.
The New Zealand All Blacks training jersey for 2013/14. Get in the Gear!
The USA Rugby Pro Alternate rugby jersey is perfect for any fan of the Eagles. Get yours to wear during the summer Test matches.
The NEW All Blacks 2013/14 jersey has arrived at World Rugby Shop. Dare to wear the colors of the All Blacks.
