I work for free with a few volunteer agencies also.
It does not pay the bills, however.
In keeping with the wx topic, suppose you were a de-icer. and what if you were asked to come in to "help out". You and I would likely do it, I, once or twice.
But, what if it became a regular thing? What if management was counting on you coming in for free on your days off, because you are a good person, and mgt wanted to save money by not hiring enough de-icers?
and what if on one of those days you made a mistake and damaged an aircraft? You are working for free and they want to ding your pay for your mistake. What do you do?
I don't know about unions, per se, but it seems you are creating a situation where you are likely being taken advantage of. Perhaps that is OK for you. But, what about the next person? Are you so desperate for a job that you are willing to sell yourself that way?
I've seen abused spouses that would make up almost any excuse to continue a relationship, as bad as it might be. Perhaps it is time you quit covering for mgt. ineptitude and start standing up for your obviously excellent qualifications.
Just sayin'