I work in mining and in this line of work, you have to be careful about expressing Democratic or liberal views. It's Republican territory. And it isn't just my workplace; it's mines all over the place that are like this.
A lot of heavy industry is dominated by Republicans to the extent that you could find yourself a pariah for being a liberal. Even a lot of warehouses are Republican dominated (I used to do mostly warehousing), but then again, many warehouses also have a lot of Democrats. Warehousing isn't dominated by Republican ideology like mining is.
Service jobs seem to be more Democratic.
Why is this the case? I think it has something to do with machismo in heavy industry, but that's not all of it.