Technically they don't.

They are somewhat obligated by the nature of their business to recommend/endorse politicians which they feel will best support the direct, short-term, narrow interests of labor. They don't attempt to look at the big, big picture (ex. economy, impact of climate politics, etc).

I'd take that as an informed input on *one* aspect of politics which may impact your job/career. You should of course weigh the bigger picture in your voting decisions, plus any other interests you have which are not related to labor politics.

Also politicians do make platform decisions based on constituent opinions and feedback... a big union endorsement, or lack thereof, will influence pols. So the union can tilt the scales a bit even if you personally don't vote that way