Per AA's 10-K, in 2024 87% of American Airlines employees were represented by a union[1]. So according to that source it sounds like the people who were fired were union members that didn't pay their dues.

They could surely have paid their dues and left the union and kept their jobs (or could have never joined the union to begin with).

[1] https://americanairlines.gcs-web.com/node/42651/html#:~:text...

I don’t know about this case specifically, but airlines frequently have different labor laws. They’ll be the exception to all sorts of unqualified statements.