Well in fact we did have a single Bargaining Unit for EBA 1 going back to the early 90's following the SEP.
The ACTU under senior Industrial Officer Les Ayres led the negotiations for wage outcome at e very senior level in Qantas. We all got the same wage outcomes and each union dealt with its own details in a series of appendices which were handed up in the AIRC by the ACTU and the relevant Union.
there was a real strength in that "Single Bargaining Unit" and the Company hated the ramifications. SO what the Company did was got a union to break away (TWU actually) and do a separate deal which broke the "single bargaining Unit". In return the TWU got a good deal in the first instance for their members and then as the unit lost grip, the rest of the unions fell like the proverbial dominos.
We now all bargain at different times, are held to ransom by the Company and have no "joint" or collective strength anymore
The only group from memory that were not part of that arrangement were AIPA as they were not affiliated with the ACTU. Ian Woods the previous AIPA president affiliated with the ACTU upon his teams election a couple of years ago.
Here endeth the history lesson