There have been very few incidents where a union successfully defended its particularistic interest in a way that harmed the interests of working people generally in the long term. Employers' associations have characterized union activity this way even when the unions were objectively losing ground in every way (e.g. declining wage shares of output, declining membership, etc).

For structural reasons, unions are constantly faced with a choice between limiting their interests to the defense of some small section of workers alone (e.g. lamplighters, software developers, truckers) or expanding solidarity with ever wider sections of the working class. To generalize for the sake brevity, unions that go the former route tend to become very weak and get captured by employer interests. Only unions that go the latter route, which requires them to adopt a broader view of their struggle, have any chance of becoming strong.

For a clear historic example in how these diverging approaches can play out, see Eley's discussion of the knife grinders union versus the metal workers union in turn of the century Germany (around page 77).

https://koncontributes.wordpress.com/wp-content/uploads/2018...