Expel from a famous trade union (4)
I believe the answer is:
oust
'expel' is the definition.
(I know that expel is a action)
'from a famous trade union' is the wordplay.
'from' says the answer is hidden in the clue.
'OUST' is hidden in the letters of 'famous trade union'.
(Other definitions for oust that I've seen before include "Expel from office or position" , "Unseat" , "Remove from a position of power" , "responsible for expulsions" , "Force from office" .)