Fair question. There's no place for intimidation. But there is a place, as I understand how it operates in the US, for advocacy. I've seen some materials from the AFL-CIO on recruiting (admittedly some years ago) but while there was a lot of material on advocacy there was nothing there about intimidation, as you would expect. If an organiser is using intimidation then they need to be removed from the campaign. But one person's "intimidation" might well be another's "advocacy".
I used to be a member of the AFL-CIO, and by Wisconsin law I was supposed to have a choice as to whether or not to join. But if I wanted the job, I had to join the union. This was accepted even though everyone knew it was against the law. One person just wasn't going to do squat to change it. But, I did tell them, in writing, to NOT use my union dues towards ANY democrat campaigns. Pissed them off but, they pissed me off forcing me to join their stinking union.
Todays unions aren't much different from any other gang of crocked thugs, which includes our government. Ta' hell with little people. It's all about those at the top getting richer, come hell or high water.