Unlike in all other representations disputes, which must be initiated by a labor organization, a carrier facing a relevant.....
So lets read carefully -
Unlike in all other representation disputes - this of course means that the single carrier status dispute is what they are discussing as this is the chapter in question
Which must be initiated by a labor organization - What they are saying here is that "all other representation disputes" mentioned above must be initiated by a labor organization.
a CARRIER - meaning the airline or railroad entity itself which has created the merger.
so to rephrase,
All other representation disputes, with the exception of the single carrier status, must be filed by a labor organization. In the case of a single carrier status dispute a carrier (airline or railroad) may initiate.......
And lets not forget the NMB regs themselves which are helpfully copied above for your viewing pleasure.
19.4 Initiation of Procedure for Determination of a Single Transportation System
Any organization or individual may file an application, supported by evidence of representation or a showing of interest (See Section 19.601-2), seeking a NMB determination that a single transportation system exists.
sheeese do you guys need lessons in English interpretation as well as spelling and grammar?