One Sandy to another,
At Southwest it is considered a "closed" shop...everyone is a member of the "union". Dues are 1%. Southwest Airlines Pilot Association (SWAPA) is an independent pilot union not affiliated with any other union group, i.e. ALPA
Being independent of other union groups is viewed by some as a big plus, others as a minus.
The "association" has elected officials at the Pres, VP, Sec/Treasury level & each domicile (7 for SWA) has 2 elected officials that represent the members at quarterly BOD meetings where they vote and decide on various issues that impact the membership (scheduling, budget, respond to various committees)...think of the committees as "staff positions" who do a lot of the worker bee "stuff", these are pilots also.
There is a permanent "staff" who are employees of the union that do the vast majority of the work & are never praised enough since they have to work for pilots

& put up with our antics as well as the ups & downs of the union, politically that is. They handle with benefits, grievances, retirement issues, communications, etc.
Unions are no doubt a "political group" that have various agendas but the goal of any union is primarily this in my view:
1. Represent the member during contract negotiations with the company by acting as the bargaining agent for ALL members (easy to say, tough to do)...the company has to have someone to negotiate with or else everyone would be paid contract employees with different pay scales, benefits, etc.
2. Act as the member's representative when it comes to the enforcement of the signed contract (your parent so to speak when you get called to the office of the principal for example)....if you have no negotiated contract (see #1) and you have no one who has the ability to persuade the company to enforce the signed contract (#2) you are rather defenseless when it comes to issues involving the health & welfare of your family & yourself.
Do unions/associations do more than the above? Absolutely. Some would argue they shouldn't, some will argue they should. Having been prior military, preconceived ideas of the pros & cons of what a union is and does goes without saying. Thinking of striking pilots marching picket lines, "following the crowd" without a choice, giving money to an organization you have no choice in are not concepts that are easy for ex-military types with normally conservative views to understand...we rebel against that type of logic.
Unions come in all shapes & sizes...they can morph from a worthwhile entity to one of chaos all due to the leadership in the company & the union/association....kind of like a squadron or a wing also....it all gets back to the relationship one has with your commander & the way he/she deals with their peers & superiors....also, leadership & who you allow into your union/company.
These are just my thoughts/comments & don't represent any fancy indoc propaganda on the pros or cons put out by SWAPA. Should what type of relationship a company's union have with the company come into play when you are choosing which airline you wish to work with? I would say yes but in today's environment where job offers are not plentiful that luxury may not exist either I realize.
The recommendations for readings listed by the previous poster are good....they will certainly give you one perspective of the labor relations between management & unions.....I will let you discern your own impression of how the history of labor/management relations relates to today's environment after you have read them. Take from all of my ramblings the following:
Union and management relations don't have to be inherently confrontational. They can be contentious at times but they should remain professional. Without a level of trust between unions/associations and management adversarial tensions increase and hinder the process of finding fair resolutions to issues that would mutually benefit both the company & union/association members.
Jetblue appears to operate well without a union and makes money....82% of employees of Southwest are represented by unions & we make a little money also...Delta is nearly completely non-unionized (except for the pilots) & they aren't doing so well....unions aren't the reasons airlines make money & aren't the reason they lose money, don't get sold a bill of goods that unions=money losers.
If you have other questions feel free to PM me but your question is a good one for new folks looking into this crazy business...its never easy to lob a question like this on anonymous forum!!! But A-10 drivers were never know to be real smart either!!
Hope that provides a little light (very little I know) and one FO's perspective on an issue that is hard for military types (I'm included in that group also) to understand. Good luck in your Airline Labor 101 study.