Labor/Trade Unions, I think, are partly a victim of their own successes (the same goes for the Trade-Union affiliated Labour Party here in the UK). There are minimum wages (though maybe they could be higher); there are reasonably protective employment laws (though maybe they could be better from the employee’s point of view); pretty much every country with the notable (and in my view utterly egregious) exception of the United States has paid family (or at least maternity) leave…
So the unions which (not unnaturally) have a vested interest in not disappearing - therefore they need to find new issues which are loosely tied to the ‘progressive’ movement they sprang from. Abortion rights, same sex marriage, etc, are two obvious examples of these.
How might these issues directly impact more “usual” or traditional union work? If an employee could be fired, or would find it more difficult to find work, for marrying their same-sex partner, because the employer has an antipathy towards SSM, that would quite obviously be something the unions would have an issue with (quite rightly). Similarly given the way employment and health insurance is tied together for many in the US, both health policies and reproductive rights (which clearly comes under that) are also areas of interest for the unions. Many union members, for what it’s worth, may well be against (eg) abortion per se, but that doesn’t preclude thinking that others should be able to make that choice for themselves (you can be anti-abortion and yet pro-choice).
Anyway, I think it’s not so much an uncritical “let’s support the Democrats/Labour Party/etc” line (Democrats get criticism too after all) - it’s not so much party-political as finding new issues to be involved in, the original ones having in some cases dried up, if you see what I mean. I’m not necessarily defending (or attacking) the AFL-CIO but from their point of view it’s probably genuine labor concerns…
