European Commission lawyers are uncertain if the stake of three major airlines in Amadeus constitutes control.
If they decide it does not, the way could be open for full de-regulation of GDSs in Europe.
The issue was raised by Michel de Blust, general secretary of the Guild of European Business Travel Agents (GEBTA).
Speaking at the annual meeting of the UK's Guild of Travel Management Companies (GTMC) in Qatar, Mr de Blust said GEBTA was concerned that the lawyers might decide that Air France, Lufthansa and Iberia did not “own” Amadeus.
The three carriers have a 46.4% stake in the GDS which is owned by a company called WAM Acquisition.
Two UK private equity companies BC Partners and Cinven own the remaining shares.
GEBTA's legal adviser Isabelle Leroy told BTE: "We don't know the situation at the moment. The lawyers are examining whether the three airlines can still be regarded as parent carriers.
"If the lawyers decide they are not parent carriers, the obligation regarding mandatory participation falls."
Ms Leroy said the definition of a "parent carrier" was "very technical" but basically related to an airline which directly or indirectly owns or effectively controls a systems vendor (in this case a GDS).
C-FARE, the organisation campaigning for safeguards in any de-regulation of the CRS Code of Conduct in Europe, said: "The Commission is asking itself the wrong question."
Its spokesman added: "The C-FARE position all along is that it's control, not ownership, which matters here, and we believe that even under the European Commission competition department's definitions of control Amadeus is indeed controlled by its airline owners.
"Things like having a veto over the budget and business plan are pretty significant, and it's clear that the airlines private equity partners are entirely dependent on Amadeus for the success of the business."
Galileo, a rival GDS to Amadeus, told the EC's directorate general for transport and energy in its submission on whether GDSs should be de-regulated that the three airlines had "effective control" of Amadeus.
In its submission, Amadeus said the legal definition of "parent carrier" had never been established and that Amadeus was "effectively controlled" by BC Partners and Cinven.
It called for the "full repeal" of the current CRS Code of Conduct.
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