No single person made the decision. That’s not how unions work; at least, not for this sort of thing. Everything is bargained and negotiated, so this was a thought out and agreed upon process.
The merging of lists is sometimes included directly into the agreement, so everyone goes in with eyes wide open. If this is the case, then it was negotiated by the union and ratified by the pilot group, so everyone who voted yes made the decision.
if the language is not included, then it is a negotiated process at the time between both the Jazz Master Executive Council (MEC) and the Georgian MEC, or their representatives - a Merger Committee. It can also be a process involving an external party. Again, either way no single person.