"Some referees are being verbally abused and are constantly having their decisions questioned. We are losing referees, and finding it harder to recruit new referees, because of this.
"Some coaches, parents, and spectators are constantly shouting at their players. Screaming 'pass' or 'tackle' at players simply turns you in to a PlayStation coach. Junior players who leave the game have highlighted this pitch-side pressure as a reason for giving up."
The letter adds that rugby's core values are under attack because even if most people on the touchline do behave they "look on and do nothing".
Greg Bayliss, the RFU's rugby development officer for the region, accepted the idea was controversial but said it was intended to stimulate debate about tackling the issues of bad behaviour on the sidelines.
He told Press Association Sport: "We have a very small problem that we want to address before the Rugby World Cup when we will have lots of people who may try the sport for the first time."
He added that Sport England had identified pressure from the sidelines as the top reason that 13-year-olds cited for giving up team sports.
- AAP