Not just union jobs, but traditionally union industries like auto workers as well. I have a friend that works in a factory in the US south. Not union, but the pay and benefits are close to keep UAW from gaining a foothold. He would complain about them handing out flyers in front of the plant every so often.

After a recent incident that had him sweating bullets over potentially losing his job for something minor (and having to face management and HR alone), I told him to take the leaflet next time. I hope he does.