An alteration to Law 3 governing the number of replacements permitted in a match came into effect on July 28, 2009 and applies to the game globally.
The alteration allows National Unions with jurisdiction over matches in their territory the option of allowing up to eight named replacements in a matchday squad.
This will also operate for cross-border club or provincial competitions with the agreement of the respective Unions involved.
If a Union allows the naming of 23 players in a matchday squad for any domestic competition, there must be a minimum of three specialist front row players within the named eight replacements comprising two props and a hooker.
Once all front row replacements have been utilised, and there is a further front row injury, and no fit front row player is available from the original starting team or replacement bench, the injured player will leave the field but may not be replaced.
This is a change to the existing laws and ensures, in playing with 14 men, that a team going to uncontested scrums does not gain an advantage.
At this stage the amendments to Law 3 are for domestic implementation only by respective Unions, but the IRB will monitor the implementation of the amended law within competitions.
The implementation will not apply to international matches.
IRB Chairman Bernard Lapasset said: "The IRB's Member Unions requested that Council investigate suitable measures to address the issue of uncontested scrums within their own domestic competitions.
"Establishing a protocol that maximises the opportunity for matches to finish with meaningful scrums, while maintaining the highest regard for player welfare and safety, was a critical factor.
"The solution needed to tackle the circumstances that lead to uncontested scrums, while ensuring that the unique shape and character of the scrum is retained.
"A process of thorough consultation and evaluation was undertaken, while a practical assessment in France demonstrated the merits of the alterations."
The model proved extremely successful in the French trials.
In 2007/08, an IRB-sanctioned evaluation in France saw the number of uncontested scrums dramatically reduced to just two in 994 matches in the top three divisions, compared to 145 matches finishing with uncontested scrums during the 2006/07 season.
The IRB works tirelessly with its 116 Member Unions and six Regional Associations to ensure the delivery of the best possible techniques for playing, coaching and refereeing this critical area of the game.