The previous post along with one or two others are very accurate.
Each ALPA-represented airline is basically a different union.
With no standard hourly pay throughout the country for a 737 or a 747, each group is on its own. Nevermind the hopeless dream of a national seniority system.
If your pilots are all either narrowbody or all widebody, your representation will cover all of the people in your company. When combined, the narrowbody pilots get sold down the river by the widebody guys who are in charge
, when Chapter 11 is around the corner. Then, the "Stockholm syndrome" among your negotiators is insidious and and is almost invisible until it is too late. We suffer because of the results.
Do not ever use pilot negotiators, except as advisor to outside, professional negotiators. It is a major mistake if your pilots are too involved negotiating.