It comes as a surprise to many that clergy can be members of a Trades Union.
I joined after a problem with the bishop and since then have twice used the Union to sort out a problem. Both went my way but I know I got a black mark.
This article sets out the case for clergy being in a union. It also, by implication, implies that clergy, especially in the Church of England, need to be employed, rather than office holders so they have proper employment rights (and duties).
It is part of the mess the CofE is in!