And the global governing body said it would be keeping a close eye on the issue during this month's international matches in Europe.
There have long been concerns players from the sport's financially poorer countries, particularly in the Pacific Islands, face economic "blackmail" by wealthy clubs in the sport's established nations.
Under IRB rules, clubs must release players at times designated for full internationals, such as the upcoming November "window", and major tournaments including the World Cup.
But clubs have tried to get round this by agreeing clauses in contracts with players from cash-strapped Pacific Island nations who then make themselves unavailable for Test duty, as happened at last year's World Cup in New Zealand.
Former Fiji outside-half Nicky Little, who has played club rugby in five European countries, labelled the practice as "blackmail".
And with the 2015 World Cup in England again overlapping with the European domestic season, the practice of clubs offering lucrative incentives to ignore Test calls could see the likes of Fiji, Tonga and Samoa deprived of key players.
Damien Hopley, the International Rugby Players' Association chairman, told Tuesday's edition of Britain's Independent newspaper: "The IRB are aware of this practice.
"It is imperative that the World Cup is defined by the best playing against the best."
IRB regulation nine forbids clubs from offering disincentives, either through "contract or conduct", to players to represent their country but critics insist officials have not done enough to enforce the rule.
But in a statement issued from its Dublin headquarters late on Wednesday, ahead of an opening weekend of November Tests including England's match with Fiji at Twickenham, the IRB said it would act on breaches of regulation nine.
"Player release is central to the integrity and economic sustainability of the international game and the IRB continues to be proactively committed to assisting (national) unions with player release issues when requested by them to do so under regulation nine," the statement said.
"The regulation is designed to deliver a fair, equitable and proportionate framework for facilitating the release of the world's best players for international duty within designated windows without impediment irrespective of country of employment.
"This regulation goes to the very core of supporting the integrity of the international game."
"The IRB takes any breach of the regulation very seriously and acts on release issues where it is formally requested to do so by a union or if it is presented with credible evidence provided by a union or recognised rugby body that would allow it to pursue its own enquiry," the statement added.
"Unions also have a clear obligation to do everything possible to uphold the regulation within their territory or they risk significant sanctions.
The IRB also said the subject of "release issues" during this month's internationals would be on the agenda for their November meetings in Dublin.