The way it was explained to me by an old timer goes like this. About 50+ years ago the pilots wanted the mechanics to form or join a union with them. The mechanics went there own way and took the cleaners and stock clerks with them. That was when it was Allegheny Airlines.
I believe it was 1949 when the mechanics and related got their first agreement, and it was with All American Airways. Don't hold me to the specific dates as I do not have the history sheet in front of me