Traditionally, only one union was active

Demarcation disputes between two unions competing for membership were
therefore avoided. Agreements reached by the union and the employers’
association were binding in respect of all relevant employees, regardless of
union membership, whilst on the other hand employers generally followed the
agreement, even if they were not members of the association negotiating it.

However, there have been a number of incidents recently suggesting changed
attitudes in the wake of long-term structural changes in employment relations.
On the employer side, there have been instances of employers withdrawing
from their association, solely in order to negotiate their own agreement with the
relevant union. It is worth noting that the thought behind this is more often
than not a desire to be more generous towards the employees than the
association wishes, in order to avoid the unrest and ill-feeling that long
negotiations can induce. On the employee side, there is a noticeable tendency
towards specialist unions representing particular skills and appealing to those
who feel themselves to be under-represented by unions representing all
employees as a body.

Perhaps the best known examples of this are the airlines
and railways, where the pilots and engine drivers formed their own unions
because they felt neglected in favour of other employees.