> This only works if everyone or the vast majority join unions.

This is a common objection but I think it's wrong. Putting aside the huge differences between US (at will) and global employment law, the idea of a fluid, frictionless workforce is quite the myth. Keeping wages down and conditions poor very much relies on the propagation of that myth that ethics will work against you. so please be careful not to do yourself a disservice (if indeed you are a developer).

In reality quite small minorities have a disproportionate impact on change. Some accounts claim it's as low as three percent. I'm sceptical of that, but the fact remains; if only a handful of people object but with severe consequences by the force of law, employers will play it safe. I find it unlikely that any employers would survive long if it transpired they were disfavouring members of IEEE, ACM, IET or whatever.