The Competition and Consumer Protection Commission (CCPC) has opened an inquiry into the GAAGO platform, to determine whether it complies with competition law.
GAAGO is a commercial company jointly owned by RTÉ and the GAA.
The online streaming service, which broadcasts hurling and football matches, attracted controversy earlier this year after several high-profile games were put behind a paywall on the platform and not made available on free-to-air television.
The CCPC told RTÉ's This Week, that it opened an inquiry into GAAGO in May.
The inquiry relates to an expansion of the service provided by GAAGO, which had previously only broadcast matches to people living overseas.
This arrangement had been cleared by the CCPC.
However, there were changes this year when GAAGO stepped in to take over the sports broadcasting rights previously held by Sky Sports.
This led to matches being shown to domestic audiences and not just to the diaspora.
On Wednesday, RTÉ's Head of Sport Declan McBennett told an Oireachtas committee that the service was currently operating without clearance from the Competition and Consumer Protection Commission.
The CCPC said it "opened an inquiry" in May when it became apparent that the activities of the joint venture "may have been extended beyond those notified to and cleared by the CCPC in 2017".
It said the CCPC "pro-actively engaged with the GAA and RTÉ on this matter".
It said mergers over a certain financial threshold must be notified to the commission whose role is to examine whether the proposed transaction could substantially lessen competition in any markets in the state.
The commission said: "When the CCPC makes a determination on a merger, it can clear it, clear it with conditions or block it.
"If the CCPC clears a translation with conditions, we or an independent trustee will monitor compliance with these commitments."
It added: "It is common practice for businesses, including joint ventures, to review, extend or change their commercial activities over time.
"In general, they are not limited in doing so. However, in principle, an expansion in the activities of an existing full function joint venture may constitute the creation of a new joint venture within the meaning of the 2002 act.
"If this were to be the case, the undertakings involved would be under an obligation to notify the merger to the CCPC."
The GAA, on behalf of GAAGO, said that it has not been formally notified that the CCPC is conducting an inquiry into the operation of the service.
A spokesman said: "The CCPC previously sought information from the GAA regarding GAAGO, a request that was duly obliged. We remain committed to engaging with the CCPC as required."
The spokesman added that GAAGO is satisfied that it is currently operating in line with competition law by broadcasting matches to subscribers based in Ireland.
He said: "However, should anything contrary to that sentiment be brought to GAAGO's attention it will give immediate due consideration to the matter."
He added that the CCPC has not made any request of GAAGO to make any changes to how it currently operates.
Chairperson of the Oireachtas Committee on Sport and Media Niamh Smyth said "it's disappointing" that an inquiry has been opened into GAAGO.
Speaking on RTÉ’s This Week, Ms Smyth said the committee had a "very robust discussion with all of the main sporting bodies" about broadcasting rights and impacts on revenue.
"It's disappointing, I'm sure, for everybody to hear there’s an actual inquiry under way, but I think it's really important that we have that openness and transparency," she said.
"I think we’re back to the very same old chestnut, if you like, about openness and transparency - and governance really when it comes down to it."
