Ignorance will no longer be an excuse for those caught betting on rugby league games, with participants made to sign a letter accepting the governing body's wagering rules by August 1.

Fairfax Media has obtained a copy of the document, which outlines the obligations of those involved in rugby league. While most players realise they are not allowed to wager on matches after several were recently named and suspended for doing so, a grey area has been the passing on of team information, such as injury withdrawals or late team changes.

Betting markets have been known to fluctuate wildly when a star player is scratched or is a late inclusion, with corporate bookmakers often getting wind of team information before it was published.

In his pomp, Andrew Johns' presence or absence in a Newcastle side could shift line betting up to 10 points, such was his influence on matches. Today's marquee names have been known to shift markets up to 6.5 points, making credible team information valuable for the odds makers or those wanting to place a bet.

However, players and administrators are expressly forbidden from passing on "inside information" to other parties according to the document put together by the NRL's chief operating officer Jim Doyle.

"You are also not allowed to provide (directly or indirectly) information about matches or teams that is not directly public," the letter stated.

"For example, this would cover providing a friend or relative with confidential information about player injuries which have not been announced. You also cannot provide inside information to a person so that they can give that information to someone else who might then bet on a match.

"As a general rule, don't provide anyone with information about your team, or the opposition, that is not already in the newspapers."

The document added that even providing updates on the "progress of a rugby league team" was not permissible. And while there was no mention of it in the correspondence, the NRL is tightening rules around dressing room access on game days to ensure players are not approached by parties looking for inside mail.

Manly winger David Williams became the face of the NRL's crackdown on player betting after he was caught betting on matches, including those he was involved in. The former NSW and Australian three-quarter was banned for the rest of the year, while several other players received lesser suspensions for betting on games they were not involved in. The NRL has made it clear the next offenders face even stiffer penalties, most likely deregistration.

The governing body, through its relationships with corporate bookmakers, can ask for an audit of betting records to determine whether registered persons have transgressed. One potential loophole has been that a player, for instance, could ask for another person to place a bet on their behalf. However, the letter clearly states: "You cannot have a friend or relative place a bet for you, or allow someone else to access an account you hold with a betting provider and bet on rugby league."

Doyle's correspondence went to NRL staff, club chief executives, players, state leagues, the Rugby League Players Association and Agents Accreditation Committee.

"The safest way to ensure that you don't breach the no-gambling rule is to never gamble on any rugby league match," the letter said.