In late 19th to early 20th century in America (and some other places), union membership actually could be a life or death proposition. Back then, violence went so far, particularly around mining industries, at times to literally be called as warfare and battles.

Examples: https://en.wikipedia.org/wiki/Coal_Wars https://en.wikipedia.org/wiki/Colorado_Labor_Wars etc.

At this point in America, push-back against organized labor (or in fact most other activism) doesn't reach this level. In some countries, however, activism of any kind is still potentially on this level of risk.