Pilot Unions
There's two (Swiss Pilots Association, ~1000 former Crossair pilots, Aeropers, ~700 former Swissair pilots) in Swiss International Airlines (Former Crossair). Instead of uniting in order to protect the Swiss pilots interests as such, Aeropers (former Swissair pilots) had embarked on a highly destructive crusade to subdue the (larger) union of the former Crossair pilots, ever since having been given a new job in former Crossair (now Swiss). This has opened the gates for management to play out one part of the pilot force against the other.
A model of how not to do it.