Let go of worker following extremists in union (6)
I believe the answer is:
unhand
'let go of' is the definition.
(unhanding is a kind of letting go of)
'worker following extremists in union' is the wordplay.
'worker' becomes 'hand' (hand is a kind of worker).
'following' says to put letters next to each other.
'extremists in' suggests removing the centre.
'union' with its centre taken out is 'un'.
'hand' after 'un' is 'UNHAND'.
(Other definitions for unhand that I've seen before include "Release" , "Physically let go" , "Let go of, remove grasp" .)